Let me tell you how good.
A lot Marvel's films are quite disappointing because they manage to either feel very repetitive or as if something has been lost in the transition to the screen, or because they dally in meaningless debates about the world's reaction to the sudden introduction of super powered beings (while never really amping up the threat level that we see in the comics universe). Guardians manages to dodge that bullet, however. In part that may be because the sandbox James Gunn has to play in is so much bigger than the conventional MCU, there are so many threats and characters he can play with because space is so big in the Marvel universe. With literally thousands of stories and characters to play with Gunn's most daunting task, I think, is finding what will work on screen and what has actual resonance. The wonderful thing is that you can feel his love for the property, and all the weirdness, flowing out of the screen. Believe me, there's a lot of love in this movie and it's there from the very start. I can honestly say the team won me from the very start and the amazing opening sequence that manages to be both a call back to the first film and to set the new status quo.
The film's plot straddles the line we had established at the end of the first film, with the Guardians doing a little bit of good and a bit of bad. Unsurprisingly that last bites them on the butt and sets the stage for the rest of the movie, leading to other characters becoming involved as a new group of aliens, The Sovereign, seek revenge for something the Guardians did. This allows Gunn to do some world building, expanding the Ravagers' role in the universe and introducing new captains to go alongside Yondu. As a fan of the Guardians' comics from the 1990s I adored the introduction of these characters, because they are the characters I grew up with (and one of the scenes in the credits really made me happy).
Characters are greatly expanded upon as well, we learn a lot about Yondu and the Guardians' themselves are fleshed out more and their relationships are particularly focused upon. Drax, for example, is allowed to show a different side to the brooding, vengeance obsessed straight man from the first film, though he is still socially awkward to the extreme. At the same time Gamorra and Nebula's relationship gets some serious expansion as we learn more about their past as Thanos' children. And of course there's a lot of focus on Peter's relationships, not just with Ego (who, obviously, is revealed to be his father - that's not a spoiler right?) but with his crew mates and Yondu as well.
Visually, the film is everything you expect from something owned by the House of Mouse. It's beautiful and often has the look and feel of something from SF classics (Ego's planet reminded me of Roger Dean's paintings for some reason, which feels pretty apt really). The Sovereign world is a study in order and serenity, Ego's world a paradise that looks too good to be true, while the forest world they crash the Milano on is dark, teeming chaos. The universe often has a pleasingly grubby demeanor. Outside of the gleaming pockets of order and future tech the clothes are dull tones (with 'Ravager red' being reminiscent of the hues Farscape was so fond of) and the technology being big and bulky. The sort of spaceships that would be graceless in an atmosphere dominate battle with tiny, zippy fighters (reminiscent in their own way with the Nova Corps ships in the last film).
The easter eggs go far beyond the references to the comics, though. Eve observed that part of the end was similar to Return of the Jedi's funeral scene. I'm sure there are far too many references for me to catch, though I imagine that fans are already working hard to compile a definitive list.
Family, and the importance of emotion, are at the heart of this film, just as they were at the heart of the first one. Gunn plays with extremes here, from one group that 'manufacture' their new citizens through genetic engineering to Ego's more sinister purpose for seeking out Peter. In the middle, of course, is the dysfunctional family that is the Guardians, with their constant squabbling and attempts at one up man ship. Even here there's a lot of love though, and the feeling that Rocket and Groot may just be the secret protagonists, both of them putting the humanoid characters in the shade and given specific chances to shine. Baby Groot is an angry little thing, constantly fighting and rampaging through the movie, beating up anything he can, while Rocket's own aggression has a scalpel taken to it in one of the most touching scenes in the film which reveals the heart of two characters.
All this is delivered with humour and grace, and the film has what is probably my favourite Stan Lee cameo, probably his last as he's said that he won't do anymore and which directly addresses a fan theory that he's actually been the Watcher all along. It's funny, fast paced and... gods I can't believe I'm saying, kickass underlying the idea that the team are BAMFs. The fight scenes are wonderfully choreographed and the twists and turns are reminiscent of Pirates of the Caribbean at its finest. The soundtrack works perfectly, too, seemlessly complimenting the action.
I urge you to go and see the film. You won't regret it.
It's the best Marvel film so far, bar none.