Isaac and Miria freaked out a little bit when they figured it out seventy years later, but adjusted quickly and had a great time, for example, being Dollars.
Tenzen Yakushiji from Basilisk has a parasite living inside his body that grants him immortality (though he's not completely immortal) and is shown to greatly enjoy it, even going so far as to gloat about it towards opponents who thought they killed him.
Tenchi Muyo! is made of this trope. The message essentially being: Immortality is great as long as you have a family of other immortals to spend it with, and you all really like each other.
In Gurren Lagann, Lordgenome spends his endless life raising kids, spawning beasts, suppressing revolts and has fun doing all three. Viral is made immortal by him and gloats about it to Simon.
Trigun leading man Vash doesn't age, and while he has a lot of angst none of it stems from this fact. He's a happy and goofy guy when his brother's not giving him grief.
Brought up by Kurt Godel in Mahou Sensei Negima!. While everyone else is busy being all depressed about how someone immortal will outlive everyone they know, the idea simply thrills him instead. No need to worry about assassination, the ability to maintain an iron grip on the world for as long as you like... However, he was in the minority opinion on that one.
All of the robots that want to eat Cashern are pissed because they were enjoying immortality and now they can't because of the Ruin.
Soul Eater: Free was imprisoned and restrained for a long time with the knowledge that not even death could free him. It was so long he doesn't remember his own name. Does that bother him? No. The first time Soul impaled him, he bragged about it.
Code Geass: C.C. was originally the other trope but after the Grand Finale no longer feels this way, because Lelouch never hated or blamed her for the tragedy that his life became, and through everything he honestly cared about her, allowing her to live out her immortal lifespan with the happy memories he gave her.
Shakugan No Shana: Considering that it replenishes his Power of Existence every night, Yuuji wonders if the Reiji Maigo will make him live forever. If this is the case he considers it a good thing because it means he can stay with Shana forever.
The elves and trolls in ElfQuest may count, since they're all either immortal or very long-lived. None of them ever seems to complain about life getting boring (some of them are too busy trying not to get killed anyway), except the Glider elves who are bored and decadent. Some of the elves do strike up bittersweet friendships with short-lived humans, though.
Notably, the bored Gliders are the oldest living elves, except for Timmain, who spent millenia in wolf form. As a wolf, she could not note the passage of time, giving her immunity to this effect.
Hob Gadling in The Sandman. Morpheus makes a deal with Hob: he doesn't die, but they meet every hundred years in the same tavern. The first hundred years, Hob tells Morpheus he got married and had a son. Second time, he's poor, his son's dead, he can't remember his wife's (also dead) name or face, he generally looks the picture of misery, the kind of guy the Pope would gladly Mercy Kill. Morpheus asks if Hob wants to die... to which Hob smiles and says "Of course not". Centuries later, when Death comes to see Hob to tell him Dream is dead and asks if he wants to die, he still says no.
Hob seems to ultimately manage because he accepts that life has both ups and downs so there's no point in despairing completely during the bad parts or expecting the good times to last forever.
The Eternal Flame from Troy Hickman's Common Grounds was the man to whom Prometheus gave fire to. It gave him power over fire and immortality. He becomes a superhero and is still able to enjoy his immortal life.
The Archons in The Secret History may go through a lot of shit, but hey, they still more or less control world events and Reka gets to bed famous men throughout history.
Vandal Savage occasionally has bouts of weariness concerning his existence, but for the most part he really gets a kick out of being an evil immortal bastard. He's got an entire world he hasn't conquered yet and enemies that are still alive after all. Most telling is that Vandal could end his immortality by refraining from eating his descendants' flesh and organs but he doesn't.
Mercury-2: "Not really. I know, you're worrying if after a thousand years a person starts getting bored with life?"
Ami: "That was one thought…"
Mercury-2: "It's sour grapes. Think about it: every single day, all over the Galaxy, something new is happening. Something new to see or do or learn or talk to. A thousand years hasn't been nearly enough."
Ami: "…But… do you ever get tired of each other?"
Mercury-2: "Well, everyone has disagreements now and then. Mars and I once spent fifteen years… well. My fault, really. But… You know how good it feels to fall in love… and how much better it gets after you've been together for a while?"
Mercury-2: "It's a linear progression. Add a thousand years."
Mercury-2: "You're just starting a very long and wonderful journey. Trust me: you won't regret it."
The Pirates of the Caribbean fanfic Jack To The Future postulates that Captain Sparrow successfully located and used the Fountain of Youth, achieved Type II immortality, and spent the next few centuries participating in various historical events. This includes both positive and negative experiences, but overall he seems to be having a good time.
Harry Potter And The Methods Of Rationality have Harry himself take this stance (and give a long list of the things he would do with his time to Dumbledore, in answer to his Who Wants to Live Forever? position), not only for himself, but for everybody on Earth. He even dreams of the very idea of death becoming a grim story that children aren't told until they're old enough to take it.
It's the whole point of its spinoff Luminosity as well.
The Great Alicorn Hunt seems to be a backlash against all the MLP: FIM fics about the opposite trope. Yes, Princess Celestia and Luna are tired of outliving everypony else, but everything else about immortality is great so they're trying to end mortality for everypony.
Discussed in The Petriculture Cycle. Twilight doesn't want to use her newfound powers to solve the story's conflict because using them would make her live forever. Penumbra, an immortal, talks her into it by, among other things, refers to a saying common among alicorns: "Mortals pass away eventually, but an immortal doesn't leave until they're ready to go."
In The Man from Earth, the immortal John Oldman makes the best of eternity, gathering huge amounts of knowledge over the centuries.
Highlander, despite being the Trope Namer for Who Wants to Live Forever?, apparently as even after thousands of years immortals are willing to kill each other to preserve their own immortality. That may be the system but they could always opt out by, you know, dying. Or, ironically, killing all the other immortals.
Casca, the eponymous mercenary of Casca The Eternal Mercenary, is rather satisfied with his immortality as a whole although he has his occasional moments of regretting it when stuck in a Fate Worse Than Death like being buried alive for decades.
Groundhog Day plays with this trope. The main character goes back and forth between enjoying and despairing over his situation. But it's a bit different from standard immortality since he's living the same day over and over which obviously has different advantages and drawbacks. He begins with hedonistic excess, then falls into despair as nothing he does means anything, then finally finds peace in deciding to be the best version of himself he can.
Jack Sparrow wonders whether immortality as the captain of the Flying Dutchman, which would mean only getting to visit land for one day every ten years at sea, is this or Who Wants to Live Forever?. Hilariously he uses rum as his criterion and tries to figure out whether a mortal lifetime with an unlimited access to rum means more or less rum than an immortal existence with access to rum once every ten years.
Davy Jones himself certainly enjoys his eternal dominion over the ocean and he sells this idea (or, more appropriately, that death is worse) to new recruits. One can presume he originally took up his post on the Flying Dutchman hoping for Eternal Love with Calypso.
Invoking this trope is one of the Duumvirate's stated goals. They refer to it as "going to the future". Their rejuvenated fifty-year-old creator strongly agrees.
Several of the Old Gods in American Gods seem to still enjoy their eternal life immensely, despite their lack of worshipers cutting their powers down to the barely-superhuman level. Most notably, of course, is Anansi, who is always enjoying life, even on those occasions when he's (temporarily) dead.
For the most part, the sorcerers of the Belgariad seem perfectly content with eternal life. This is in part because they keep very, very busy. (One, Senji, doesn't even notice he's immortal until he takes a break from trying to turn lead into gold and realizes several centuries have passed.) Not all of them were so content. Of course, those ones are not around anymore.
And those who hated their life usually had another reason than immortality to hate it. For one, it was the horrors of war.
Peter Pan milks every bit of fun out of eternal youth. It probably helps that his memory spans an average of five minutes.
In Twilight Bella finds no qualms at all to be spending all eternity with her teenage husband and super-quick aging daughter.
Tarzan and a few of his friends attain eternal life and youth by stealing some immortality pills from one novel's Big Bad (he cannot share immortality with the world, due to the pill's morally dubious manufacturing method). Tarzan has a very upbeat, "seize the day" mindset and is completely unbothered by the consequences of his immortality. When asked by someone if the thought of all his friends growing old and dying bothers him, he replies that the promise of making new friends makes up for it. When asked if he is worried about boredom, Tarzan replies that he lives such an exciting life, he doesn't worry about it.
In Aleksandr Zarevin's Lonely Gods of the Universe, not one person (either human or Ollan) who has become immortal after eating Ambrosia (it's a plant, not a drink) regrets being mortal. Yes, women become sterile (see Immortal Procreation Clause), but they don't really care. Men can still father children with mortals (and have). Their lives get even better after they eliminate monogamy among themselves (at the women's request) and just have giant orgies. They have a limited supply of Ambrosia and no way to get more, so they have to hand it out sparingly, but one full dose is enough to heal any injury (even regrow lost limbs) and restore youth, as well as grant eternal life. A partial dose will only do the first two.
Not quite living forever, but pretty much everyone agrees that Prolong, an anti-aging treatment in the Honor Harrington stories which extends the active human life to around three centuries is pretty damn awesome. Amongst other things it lets you spend fifty or so years in a Naval career and still have over two centuries left to do other things if so desired.
In the Iron Druid Chronicles Atticus is more than two thousand years old and he is still enjoying his life enormously. It helps that he is an earth druid so he has a very close bond with nature which grounds him and preserves his sanity. The werewolves also seem to enjoy their long lives.
The Others in Night Watch almost never have regrets about their unnaturally long lives. However, most of them try to avoid having children so as not to have to watch them grow old and die. An Other's child can become an Other, but this has about as much chance of happening as an Other born from Muggles. The only exception are vampires and werewolves, who turn their children, but they are the lowers of the low in the Dark Other hierarchy.
Sergey Lukyanenko: in his short story "I'm in no hurry", a Genre Savvy student summons a devil and offers his soul in exchange for infinite wish fulfillment. As a side effect, a deal made him completely immune to age, harm and restrictions to action or communication, except for those caused by the wish itself. Decades later, the devil finally freaks out about his master (now world-famous, wealthy scientist, still looking as the man in his prime) never making a single wish. The professor reveals that he feels pretty cabable of achieving anything he wants on his own, and all he needed was an unlimited (and youthful, and And I Must Scream-free) time.
Fablehaven: There are 5 immortals who all function as Barrier Maidens. Two aren't identified and killed offscreen, Marcus is Who Wants to Live Forever?, Civia regards her immortal life as a duty which she always regards as important. Roon, though he died offscreen like the first two, was said to have enjoyed his immortality. He formed a hunting pack of the finest men to go go and hunt various dangerous monsters, and was described as a Boisterous Bruiser. His body is found amidst the bodies of his attackers and allies, his familiar even suspects that he would have won the battle if not for the enemy having magic.
Adventure Hunters: Gargoyles live for a very long time, and since many of them are historians, they find this very helpful.
Live Action TV
The Doctor in Doctor Who experiences a lot of heartbreak, but still feels that life is worth living so long as there's something left to see in the Universe. Also, the Face of Boe, to an extent.
In Torchwood, Captain Jack Harkness in general. Sure, he has ocasional angst over it, but considering his average deaths per episode count, he sure is getting his money's worth out of the deal. Also, more time to go hit on people.
Inverted in The Miracle Day arc, where (almost) everyone on Earth becomes unable to die. Even suicide bombers are still alive, despite being charred beyond recognition. Also, while people stop dying, no one stops aging. Inversely, Jack loses his immortality and has the time of his (very long) life, although now he insists on using condoms.
The Middleman has Cecil Rogers, in the episode "The Cursed Tuba Contingency". He's been cursed to wander the earth unaging ever since he kicked some people out of a lifeboat on the Titanic, and says that, he thinks this is pretty neat.
A good number of Immortals in Highlander: The Series seem to be having a grand old time; sure, they have problems, but they still enjoy their lives. The protagonist is a major exception — but he'll still fight tooth and nail to survive. He only seems to regret being immortal when something really bad happens in his life.
In Can You Live Forever?, Adam's greatest regret after his first thousand years is that his children all died before his 132nd birthday. However, he loves to show off his collection of awards and spare bodies.
Buffy the Vampire Slayer: The greatest difference between Spike and Angel is that the former believes in this trope. He even vamprized his mother so that between her and Drusilla he'd never be lonely.
There's a human turned robot in Star Gate SG 1 who refers to this trope as "The Gift". For context, he is trapped in a facility that's constantly falling apart because if he left his body would run out of electricty within hours. He spends all his time fixing problems or checking for problems. All alone. Even after living this way for centuries he still considers immortality a good thing.
Dead Like Me: Played with. Unlike the other reapers who are angsty or apathetic, Mason's pretty happy with his lot in death. On the other hand he envies the souls that get to pass on while he has to stay behind, but this is because whatever's on the other side is better than the side he's on.
Star Trek: The Next Generation: The opinion of his race as a whole but Q in particular believes this trope. One of the most severe punishments they have (and sentenced Q to once) is to make one of their own mortal.
In The Legend of Maian, most of the Regis Knights, immortal super warriors who can't die till their -also immortal-master dies.
I am immortal. I have inside me blood of kings. I have no rival. No man can be my equal. Take me to the future of your world!
The song "Immortal" by Clutch makes it sound pretty awesome:
Who's the man who stole fire for the people? Who causes trembling in the bones of evil? Who carved a mountain into a cathedral? I am immortal.
The backing lyrics for the chorus repeats the phrase "in dog years," suggesting the narrator isn't immortal—at least not literally.
The Brazilian song "Eu nasci ha 10000 atras" (I was born 10000 years ago) by Raul Seixas is (obviously) about a man born 10000 years ago who talks about famous events he witnessed. He sounds very enthusiastic about his life:
Eu nasci há dez mil anos atras... (I was born 10000 years ago) ...Eu vi Cristo ser crucificado... (I saw Christ crucified) ...Vi Babilônia ser riscada do mapa... (I saw Babylon be wiped off the map) ...Eu vi conde Dracula sugando sangue novo... (I saw Dracula drinking blood) ...Eu tava junto com os macacos na caverna...(I was with the monkeys on the cave) ...Eu vi a estrela de Davi brilhar no céu (I saw the Star of David shine in the sky)
The long-lived and nigh-immortal Eldar of Warhammer 40000 fight tooth and nail to survive. Granted, it's not so much that Living Forever Is Awesome but rather that dying is much much worse. If Eldar are lucky they will have their souls trapped in crystals for all eternity. Otherwise, they become the playthings of the Chaos god Slaanesh.
The Mummies of the Old World of Darkness are generally of this opinion. They might live in a Crapsack World and have often difficult battles against terrifying foes but hey, they have literally all the time in the world to put things right and plenty to enjoy along the way.
The Longevity Vaccine and Clinical Immortality projects from 'Sid Meiers Alpha Centauri, The Longevity Vaccine will eliminate 1 to 2 Drones and/or boost your economy by 50% based on your economic model, and Clinical Immortality nets you a free Talent at every base plus 50% more votes in elections. It helps that these are presumably widely available treatments, meaning everyone lives forever and the worst aspect of Who Wants to Live Forever?, the losing people you love, is not a problem.
"I plan to live forever, of course, but barring that I'd settle for a couple thousand years. Even five hundred would be pretty nice."
— CEO Nwabudike Morgan, Morganlink 3D-Vision Interview
Interestingly, the novelizations claim that the treatments are only available to the higher-ups. This handwaves why the faction leaders are still alive after centuries of rule.
The guy who constructs the training courses in Immortal Defense seems to think this. Even as all the other path defenders go insane one by one and start leaping across the Moral Event Horizon. It helps that path defenders tend to go insane because they fixate on something and will go to any lengths to protect it; he ended up fixating on...constructing training courses.
Many characters in the Touhou series are happy with their immortality.
Yuyuko used her superpower of instant death to (somehow) permanently remove herself from the cycle of life and death, trapping her in the netherworld to seal a world-devouring evil spirit in a tree, and now lives quietly whenever she isn't causing trouble to sate her boredom. Although her canonical Crouching Moron, Hidden Badass nature makes it hard to tell for sure, she seems to generally enjoy her eternal un-life, especially when it comes to teasing her overly-earnest subordinate, Youmu.
Shiki Eiki Yamaxanadu and Komachi, as judge of the dead, and ferrywoman of the equivalent of the River Styx, never really seem to complain about "outliving" everyone they know, but then, being Anthropomorphic Personifications of death and rebirth, and the knowledge of how the afterlife works may give them a radically different perspective on the whole thing.
Kaguya and (probably) Eirin, seem to be enjoying immortality quite a bit. Kaguya seems to mostly suffer from boredom, but has had Eirin taking care of her essentially her whole life. She also has mortal, if extremely long-lived servants, but she seems not to care about them to the point of calling any and all of them "Inaba", rather than learning their names.
Fairies may have the most amusing of all immortalities — they are functionally immortal as long as the force of nature that they represent still exists. They, however, are all permanently child-like, and spend all eternity playing pranks on one another, don't bother with notions like owning any property they don't wear on their backs (if clothing doesn't just magically appear on them in the first place, it's not like they would manufacture all the frilly dresses they wear) not really understanding the difference between yesterday and ten thousand years ago.
To be specific, they have Type IV immortality: they simply regenerate after being killed.
We could've made this list so much shorter simply by stating that the only character who isn't of the opinion that immortality is awesome is Fujiwara no Mokou, who's lifestory goes something like this: Father got disgraced by above mentioned immortal Kaguya, Mokou drank the Hourai elixir to get a fair shot at Vengeance, got ostracised when people eventually noticed her unchanging appearance, became a hermit and lived alone for quite some time, went absolutely Ax Crazy for two-hundred years and proceeded with killing anyone and anything that came in her way, went into a bit of a decline and lived in an apathetic depression for a few hundred years, finally found her way to Gensokyou where she found Kaguya again, re-ignited their rivalry and has since then spent the time locked in an eternal circle of revenge murders with her arch-enemy. It's not so very weird that she really regrets drinking that damn immortality potion, is it?
Soul Calibur - Zasalamel, who had previously been all about Who Wants to Live Forever?, gets to see a vision of mankind's far future in the fourth game and decides to keep his immortality instead of ending it to see the advance of mankind. We get a scene of him as a rich businessman with a helicopter in the 21st century in the end.
When Parsec the Fire Dragon asks Aphelion the Silver Dragon why he defends the humans, his reply is pretty much 'it's unfair that dragons and elves get to live forever when humans don't.' His ultimate goal involves extending his own immortal life.
In World of Warcraft the High Elves (by way of the Well of Eternity) and one of their descendent branches, the Night Elves (by way of the World Tree), were contentedly immortal for well over 10,000 years (not including the whole War of the Ancients thing). Many Night Elves were rather sad to lose their immortality due to the events of Warcraft 3, and though it was a necessary sacrifice World of Warcraft opens with the Night Elves trying to regain their immortality through the creation of a new World Tree (the attempt does not go as planned).
The Draenei appear to be functionally immortal (they do not seem to die of old age) and their leader, Valen is at least 100,000 years old. Immortality does not bother them at all.
Sylvanas Windrunner used to be all Who Wants to Live Forever?, but after getting a taste of The Nothing After Death all evil Undead are doomed to visit when their undeath ends, she's decided that an unending undead existence isn't that bad in comparison.
Glados's final song in the end of Portal 2 has a tinge of that*
One day they woke me up/ So I could live forever/ It's such a shame the same/ will never happen to you
, though many speculate that it hides her bitter hatred at her own existence and that she just sent the closest thing she had to a friend away.
Most of the Daedra, especially the Daedric Princes, of The Elder Scrolls series rather enjoy their immortality. A good example is Sanguine, who basically just lives to have fun. His quest in Skyrim could be described as an Elder Scrolls version of The Hangover or Dude, Where's My Car?.
Variation: Cucuvea the mystic believes she would have had this attitude... had she been able to spend her immortality anywhere other than Transylvania. Living in an extremely damp hole under a tree, obligated to defend the local villagers, and under constant threat from roaming vampires and werewolves, she's not exactly having a good time.
Forerunners of Halo wear armor that effectively stops aging, among other things. Aside from a few "naturalistic" ones, this applies to their entire society, so it's less "Living Forever is Awesome" and more "Living Forever is Normal". They are capable of dying, but this is exceedingly rare, aside from the lowest rates with dangerous jobs.
You know in those stories there's this immortal guy and they talk about how bored they are and how boring life is after 5000 years or whatever? I am going to call something. I am going to call SHENANIGANS.
The Kingfisher: Most of the vampires in this comic show no signs of boredom or guilt at the prospect of immortality. Dragomir vampires especially seem to enjoy eternal life.
Not awesome per se, but the narrator of The People I Have Been from The Wanderers Library seems quite happy with his arrangement, saying “I've been a soldier and a minister, a leader of men and a follower of causes. I've preached hellfire and harmony. I've said words profane and holy. I've been people I didn't like, and people I wish I could be again. But that's life, Emma. Life isn't static, it isn't frozen. Life doesn't stand still. It changes, and it changes us. This is just another step.”
Demona has lived for centuries and there's not a trace of weariness or boredom to be found. Macbeth, who became immortal at the same time, lives only to kill her so that he himself may die. Eventually, though, he finds something else to live for.