These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Draco in Leather Pants: A lot of adaptations, such as John Gardner's Grendel, the 2005 film Beowulf and Grendel, and the 2007 film, tend to portray Grendel sympathetically, despite the fact that in the poem, out of the three monsters, he's the one the narrator condemns the harshest and the most often.
First Installment Wins: The first portion of the story is the most familiar to the layman, including such well-known elements as Beowulf's having the strength of thirty men and ripping Grendel's arm off.
Ho Yay: In Seamus Heaney's translation, Hrothgar's farewell to Beowulf seems extremely... intimate.
To the Anglo-Saxons, Beowulf would be a perfect hero, representing all that the Anglo-Saxons stand for. To modern readers, Beowulf can come off as a selfish, arrogant person who perpetually seeks fame.
Although the text repeatedly conveys that Beowulf's defeat of Grendel was a noble act, the description of the scene is so bone-crunchingly brutal that it makes Beowulf look downright sadistic. You almost feel sorry for Grendel. This is part of the reason that more people are making Grendel a Draco in Leather Pants in modern times. The mere fact that Grendel is a descendant of Cain would've struck most Anglo-Saxons as reason enough for Grendel to be deserving of his miserable life in the swamp- to a modern reader, punishing someone for their ancestor's deeds just comes across as petty.
Woolseyism: Seamus Heaney's translation. On the one hand, it was done by a Nobel Prize-winning poet, so it reads very well to say the least. On the other hand, he took a lot of liberties with the text, such as anglicizing the name "Scyld Scefing" to "Shield Sheafson." Needless to say, there's a Broken Base on this one.
One instance was to enforce a One Beowulf Limit — both Scyld's son and our hero are both called "Beowulf" in the original, and so Heaney changed the former's name to simply "Beow" for clarity.
The Woobie: Poor, poor Hrothgar. You just want to build the next wonder of the world, and for years to come a monster is feasting on your men, and you know you can't do anything about it. When you finally get rid of the monster, another one comes and kills one of your best warriors. When that one is taken care of, you're so grateful towards the hero that did it that you hope to meet him again, but know that you won't because you're dying, and after you're dead, your prized hall is destroyed and your nephew, who you hope to watch over your sons, ends up killing them. Hrothgar's life sucks.
Evil Is Sexy: Grendel's Mother. Profoundly averted by Grendel himself, though.
Family-Unfriendly Aesop: Stories of heroism are basically lies told in order to cover up questionable or outright shitty behavior, and by the time you realize you shouldn't have told the story in the first place, you'll be too old and filled with regret for it to matter. This isn't entirely untrue - see Plato's Republic for more on the dangers of "true" heroic stories.
Nightmare Fuel: As Grendel's Mother lays Grendel's body to rest, she is humming and quietly sobbing. Eventually her wailing degenerates into an utterly blood-curdling shriek that echoes throughout the mountains. Grendel's Mother is the original Mama Bear in Anglo-Saxon folklore, and a viewer knows then and there that she is pissed beyond all reason and is coming for revenge.
Older Than They Think: This film is often accused of plagiarizing 300, with the line "I! AM! BEOWULF!" being a bit too similar to "THIS! IS! SPARTA!" and the line "TONIGHT! WILL BE DIFFERENT!" being rather akin to "TONIGHT! WE DINE! IN HELL!" What these people don't realize is that there's a thing called Animation Lead Time. Filming of Beowulf was done long before filming of 300 began.
Stoic Woobie : Wealthow verges on this when she looks a bit sad at the beginning of the movie.
Tear Jerker: The loss of Grendel's arm. Instead of just ripping it off, Beowulf pulls it taut with a chain and crushes it off by slamming Herot's door on it repeatedly while Grendel desperately tries to tell the Geats that he's not a demon and cries in fear as Beowulf screams at him.
They Just Didn't Care: Robert Zemeckis openly expressed his hatred for the poem on which it was based, so all the nuance and meaning of the poem is completely ignored, radically changing the story and essentially making it an In Name Only adaptation.
Uncanny Valley: A bit disturbing at first, but gets better as the film goes on. Clearly, the crew learned a few things from The Polar Express. For the most part, the expressions and characters themselves don't invoke this a whole lot. But there is a slightly creepy air whenever they're prominently handling objects or interacting with them, due to the objects not seeming to have any weight and simply "float" in the characters' hands.
Villain Sue: There does not seem to be any way to harm Grendel's mother. The method Beowulf uses to kill her in the poem was never tried or even hinted at, so that might still be a viable option but we otherwise have no reason to believe the movie version is anything but invincible.
What Do You Mean, It's Not for Kids?: Director Robert Zemeckis had originally intended to release an NC-17 version for IMAX theatres and a PG-13 version for regular theatres but was forced by Paramount to deliver an R rating. The final version was rated PG-13, which surprised many people on the production (including Angelina Jolie, who did not see the film as family-friendly and refused to let her children see it).