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.
Award Snub: Goodfellas, Scorsese, and Braco lost to Dances with Wolves, Kevin Costner, and Whoopi Goldberg for Best Picture, Best Director, and Best Supporting Actress, respectively. In hindsight, Goodfellas is considered Scorsese's Magnum Opus. On the other hand, Joe Pesci not only got a fully deserved Oscar for Best Supporting, he didn't even expect to win and gave one of the shortest and most modest speeches in Academy history ("It's my privilege. Thank you.")
Ray Liotta wasn't even nominated.
Also snubbed was Thelma Schoonmaker for Best Editing. The fast-pace editing of Goodfellas was controversial at the time but in hindsight it's considered one of the most expertly edited films of the last 30 years.
For some (most notably, Roger EbertandGene Siskel), the loss for Best Director was particularly galling. Kevin Costner was already listed as a co-producer for Dances With Wolves (the heavy frontrunner for Best Picture), so it seemed redundant for the Academy to honor him again as a Director over Marty, especially given how much the latter's direction really shines in Goodfellas. To make matters worse, Wolves was Costner's film debut, and many already thought Scorsese was due for recognition after losing out for Raging Bull against Robert Redford and Ordinary People (and, fittingly enough, Redford had beaten Marty for a directorial debut, also).
Awesome Music: The whole soundtrack, or at the very least, all the classic rock.
The part where Jimmy is seen smoking at the bar while Sunshine of Your Love by Cream plays. Pure badass.
The way the instrumental coda to Layla is used during the montage revealing the fate of everyone involved in the Lufthansa heist.
Film critics point to the mix of songs during Henry Hill's worst day - Jump Into The Fire, and Mannish Boy in particular - as the best use of period soundtrack ever.
Darkness-Induced Audience Apathy: The movie itself made it hard to say whether or not you should care about Henry himself, alongside with the other gangsters, Tommy and Jimmy included, throughout the movie itself.
Magnum Opus: Regularly in the running (along with Taxi Driver and Raging Bull) as Marty's best film. Given how much the former two strive to be dark character studies, Goodfellas is probably the most "re-watchable" and entertaining of the three.
Wangst: Having watched Henry become a major player in the Mafia, act as an accomplice in several major crimes (including murder and a major armed robbery), become a drug dealer, abuse his wife and eventually rat out all his friends and colleagues, it's hard to feel too sorry for him at the end when he whines about the fact that, now that he's in Witness Protection having escaped any prosecution and even mob retribution for his crimes, he's no longer a bigshot.
This might be intentional to keep him from being too much of a Karma Houdini- the punishment seems light to everyone else, but it's torture for him. Compare his "Egg noodles and ketchup" complaint about the misery of living life as an "average nobody" to when he was in prison as a wiseguy and eating like a king every night.
What an Idiot: Jimmy wants to put a hit on Henry at the end because he is worried Henry'll squeal to the cops. It's the realization that he has a hit on him that makes Henry squeal in the first place.
Note that despite the What an Idiot aspect, this really happened on several occasions.
Henry's exposition about his drug mule/babysitter; she is insistently told to leave the house in order to make a drug related phone call. And what does she do? She phones from the house. The narcs of course are wiretapping everything.
“So, what does she do after she hangs up with me? After everything I had told her? After all her yeah, yeah, yeah, bullshit? She picks up the phone and calls from the house. Now, if anybody was listening, they'd know everything. They'd know that a package was leaving from my house and they'd even have the time and the flight number. Thanks to her.”
The Woobie: She may be a stereotypical overbearing Jewish Mother but Karen's mother is completely right about Henry, albeit for the wrong reason, and in the end she loses her daughter to the Witness Protection Program with no promises of ever seeing her again.