Okay, Guardians of the Galaxy is one of Marvel's less-known comics. It features a bunch of misfits who get together to save the galaxy and they eventually get a name for themselves in the comic. Also, rocket was famous enough that he eventually went on to star in Ultimate Marvel vs Capcom 3, so at least one of them is pretty popular on the net.
This film sort of tells the story of how the Guardians of the Galaxy comes about in the film-verse. If you've seen one misfit movie, you will know the basic plot and resolution of this film because it really doesn't deviate from that formula. The characters are still fairly close to being archetypes with (from left to right) the Rogue; the Stoic warrior, the female warrior, the chaotic evil guy and the silent but gentle giant, and they don't really get enough development in their own rights to break out of that archetype. But considering this is the first film they've appeared in and they haven't had the benefit of previous solo films to establish their character, this can probably be forgiven.
With that being said, Guardians is pretty much the prettiest film in the Marvel film-verse. The CGI and effects that went into this show are stunning and it easily beats everything else hands down. Including Iron Man in my opinion. While the Iron Man CGI is very impressive, the animation usually only included the Iron man suit. While in the GotG film, entire sets/locales are animated in a very visually stunning way. It even beats Thor hands down because Thor only really had Asgard in terms of CGI animation. I don't really consider barren wastelands to be a great visually stunning CGI effort.
The film does suffer from very mediocre fight choreography though. At least for the hand to hand combat. When the fisticuffs aren't exciting but seem more routine, then you know something has gone wrong. The spacefights are interesting for what they're worth but it's really just one giant spaceship vs a bunch of smaller spaceships, who can barely even hurt it.
In terms of casting, I'd only really have issues with two of the casting choices. One is Lee Pace who played Ronan. In his full costume, Lee Pace looks more like an emo goth cosplayer than what I would imagine Ronan the Accuser to look like. Also, Ronan always struck me as a lot more muscular than Lee Pace. He's more like a Rock, or a Hellboy or a Bane type of figure. Basically a very bleh costume as well. Not too ecstatic about what they did to his character either. Ronan started off as a huge dick in the comics but the Annihilation wave arc really polished his character and he was actually pretty decent by that time.
Secondly is Zoe Saldana. I have no idea if it's the lack of eyebrows + really pronounced cheekbones that's doing it but it just looks really weird. Especially when the comic book Gamora looks like that and actually HAS eyebrows. I'm not sure, why was there a decision to make Gamora eyebrowless? I mean, when a comic book character has eyebrows, there has to be some special warped way of thinking that makes people go 'oh, the film version will have NO eyebrows'. It's literally a more extreme step away from turning Kingpin into an African-American or Goku into a white american.
The movie does have a lot of plot contrivances though. Like the collector suddenly not securing the Time Gem so that his assistant can try to steal and then cause a catastrophe which leads the Guardians to realise they need to keep the gem safe. Or when Ronan gives the GotG their team name. Or when Ronan is about to destroy the Xandarian home world and Starlord does something so utterly stupid to distract him that you have to watch it to believe it. Yeah, things like that.
Speaking of Xandar, I was kind of disappointed Richard Rider didn't make an appearance in the movie. Or that they totally changed the concept of the Nova Corps. Again, I took a real shine to the character during the Annihilation wave arc.
Overall, this movie isn't bad. It's just not as great as it was hyped up to be. In terms of Disney Marvel movie rankings though, I would put it above Iron Man 2-3, Thor 1-2 & Captain America 1; with Captain America 2 being no.1 on my list.