Warning: nerd thread.
There are a few top tier Marvel films.
They vary of course from person to person, but among the people who like these films, "The Avengers" and Cap 3 are the two most mentioned, with some mentions of Iron Man 1 and Cap 2.
I believe that the Avengers and Cap 3 are the best Marvel as to offer, but I think 3rd place and very close on their heels should be "Thor." Thor is such a complex character with like 60 years of comic history along with an actual Norse mythology that director Kenneth Branaugh did a phenomenal job making this story breezy, adventurous, and wholly different from every other origin story in the Marvel cannon (note: I have yet to see Doctor Strange).
I'll offer 5 reasons why.
1. The movie is perfectly cast and perfectly acted.
Chris Hemsworth as Thor is, with the possible exception of RDJ as Stark, the single best casting decision Marvel has made. Nobody else on earth could nail the look, charisma, and comic otherworldliness that Hemsworth imbues Thor with. Hiddleston as Loki has been so ****ing good across three movies that he's the only Marvel villain that's even registered. Natalie Portman has a shit job in this film but does a really solid job with it (she actually cared in this movie -- she justifiably lost interest around the time of Thor 2 and is now out of the MCU). The Scandinavian guy who plays Dr. Selvig is fantastic, just everyone is amazing.
But none of them compare to what could have been a very droll, Jesus-like role in Odin, which Anthony Hopkins destroys. Every single thing he says could have been delivered in the most boring way possible, but even when Hopkins is instructing young Thor/Loki on what it means to be king, he sells it.
2. The fight scenes are pretty scarce, but are more inventive for Thor.
Branaugh so thoroughly nailed the nature of Mjolnir: it is a universal-caliber weapon because it is incredibly powerful and magically-driven, yes. But it's also incredibly versatile in ways no other Marvel film has displayed it.
In Avengers 1, all Thor does is beat people with it, like a regular hammer. Same in Avengers 2. Same with Thor 2. Sure, he flies with it. But in "Thor," you see the full scale of everything Mjolnir can do in battle. It whacks people, it can summon lightning, it can kill but both throwing it and calling it back. It can pin people down. It can skip rocks through people. It can fly through a gigantic monster's skull. It can summon a tornado and destroy the Destroyer by overheating its frame, using its own lazer (or whatever) attack against it. At one point, he exposes the "real" Loki from all the replicas by zapping him.
It also features a fight scene where he just manhandles two dozen SHIELD agents.
3. The movie's score is amazing.
Easily the best Marvel's done.
4. The writing is outstanding.
The downside to there being so many Marvel films is that the dialogue does start to sound similar throughout them. But Thor's movies are, of course, somewhat different, because the characters speak in a Shakespearian cadence throughout the film (Whedon does a great job mimicking this in the Avengers, though his touch wears off in Avengers 2 and Thor 2 totally butchers it). Branaugh directed the best ever "Hamlet" put to film, by the way, so this is a perfect tonal match for him.
It does create beautiful turns of phrases that would be ordinary discussions in regular Marvel films but become cryptic declarations. When Odin answers Loki that "you are my son" -- Hiddleston nails the remark "what more than that?" Thor's speaking style is also great when he's stranded in New Mexico -- "how DARE you attack the son of Odin!" is hilarious as doctors try to care for him. Everything Idris Elba says as Heimdall sounds like silk.
It also serves the regular English speakers in New Mexico well. One of the best (and most underrated lines) of the film comes from Selvig, who passes out drunk saying "I still don't think you're the god of thunder, but you ought to be."
5. Aside from the unfortunate love story, every decision in the film is pitch perfect.
i. In the comics, Thor is actually David Blake, a regular doctor who then discovers one day he's Thor. The movie wisely starts out with Thor knowing he's Thor, owning all of Asgard, until his fall from grace.
ii. The call out to David Blake is great.
iii. The greater MCU, aside from the ever-present Agent Coulson, only has two quick mentions, but they're both great: one is Coulson saying he doesn't know if Tony Stark made the Destroyer, and the other is Hawkeye training his arrow on Thor while he storms through the SHIELD compound.
iv. The fact that Loki wants to destroy Jotunheim not through conventional warfare but by firing an interdimensional bridge at them is clever and forces Thor to make a harder decision than simply some regular punch-'em-up.
v. The film embraces the Norse mythology in the smartest way possible: Dr. Selvig is Scandinavian, and was read these stories as a child. Turns out the stories are true, and based on actual Asgardian gods that came to earth millenia ago.
vi. Thor's explanation of how magic works is written so well: "I come from a world where magic and science are one in the same."
vii. The opening shots of Asgard are pretty cool, as being this strange inverted kingdom on an actual planet across untold explanses of space connected by a mythical tree of "realms."
viii. Kat Dennings is hot but unfortunately we don't even get to see her cleavage in any Marvel films -- that's not an argument for "Thor" but deserves to be complained about.
ix. Thor orders a dog or cat at a pet store that's "large enough for me to ride."
x. The special effects aren't too amazing, but there are some brilliant cinematography, particularly the super high-def shot of raindrops falling off Thor's face after he failed to lift Mjolnir at the SHIELD compound.