Please, everyone, take a moment to bask in the fact that we live in a time when a character like Rocket Raccoon can be fully realized on the big screen.
"Guardians" is a comic book film unlike any of the comic book films we've had since the recent resurgence of comic book films began. While many of these movies have had elements of comedy (Hulk, smash!), "Guardians" is the first to really be a comedy first. There are fights and drama and techno-sorcery in abundance, of course, but what you'll leave "Guardians" remembering most is that it's pretty funny.
Not high-brow funny. But wordplay funny enough that it was entertaining as a comedy. It's true that there are only so many times "I am Groot" can be mined for laughter, and a foul-mouthed raccoon only gets you so far, but Star Lord's enthusiasm and wit make the script a breath of fresh air for the genre.
Star Lord is a character born of tragedy, like so many good superheroes are, but while it's an important element of his backstory, it doesn't completely define him.
Surrounding him are the cast of misfits you've seen from the trailers, and you could guess that Rocket and Groot are the stand outs. They're given the most to do, and the most developed arcs. The other Guardians are fine, for what they need to be.
My issue with Marvel's "cosmic movies" has always been the villains. With the exception of Loki, whenever Marvel heads to space (or Asgard, or whatever), we get villains covered in makeup and techno-medieval armor with no motivation other than to destroy. That's no different here, really, though Ronin is a more compelling villain by far than that dark elf guy from "Thor 2."
Still, I appreciate Star Lord's attitude. He wants to be a hero, not out of honor, or reluctance, but because, primarily, it's fun saving the galaxy.
Because I always view things through the eyes of a dad, I'll say that "Guardians" is pretty safe for a late pre-teen viewer. There is some light swearing. The violence is bloodless, and when the Guardians are fighting the space police, it's with knock-outs, not killing. They may be outlaws, but they're still the good guys.
Mild spoiler: there was no mid-credits scene in my showing, but there was a post-credits scene. It was worth staying for the harming of animals disclaimer near the end of the crawl.
I'll give "Guardians of the Galaxy" four I-am-Groots out of five.