Marvel is either really worried about Guardians of the Galaxy or totally gung ho. You really can’t forgive them for being slightly worried since the movie is based on one of their lesser known comics series filled with characters who aren’t Iron Man, Thor, Captain America or any of the other Avengers. So what better way to get the public excited about the movie than to present 17 minutes of the film at a special IMAX 3D screening?

What it does have is the vilain Thanos, whom we got the briefest of glimpses of at the end of the first Avengers movie but has been missing in action ever since. But Thanos will be the big bad of Guardians of the Galaxy as voiced by Josh Brolin. The film also has Chris Pratt, the unlikeliest of actors to play a Marvel hero, but we’ve all seen his new, buff physique so he’s actually pretty perfect for the role with his ability to play the dim but likable hero.

The special preview introduced us to Peter Quill (Pratt), Gamora (Zoe Saldana), the adopted daughter of Thanos, Drax the Destroyer (Dave Bautista), Rocket Raccoon (Bradley Cooper) and Groot (Vin Diesel), a walking, talking tree which only says, “I am Groot.” Peter, Gamora, Rocket and Groot are prisoners being transported to The Kyln, a space prison. The prisoners already know Gamora and her connection to Thanos, and are eager to exact some justice on her.

The main gist of the preview was the big escape of the four convicts, aided and abetted by Drax. The scene was full of amazing visuals, from the design of The Kyln to the various inmates, and some very funny dialog. Where there was a bit of humor in the past Marvel movies, it’s clear that Guardians of the Galaxy will lean more towards the comedic side. Peter, aka Star-Lord, is just a funny character with his dim-bulb characteristics, so the humor comes out of him naturally.

The real stars of the preview, and one is to assume they will be the film’s breakout stars overall, are Rocket and Groot. When it was announced two of the characters were a talking raccoon and a talking tree, most people felt that Marvel was taking a huge risk and might see their first stumble. But Groot, even with his limited vocabulary, was pretty funny because of the inflection of his voice (and Rocket has the ability to translate those three words into full sentences). And even though Vin Diesel is doing the voice, it really doesn’t sound a whole lot like him. He really won me over.

Rocket, as voiced by Cooper having a great time, completely steals the show. The CGI character, played by director James Gunn’s brother in a motion capture suit, is fully realized and Cooper gives him a real personality. Rocket isn’t actually a raccoon, but a genetically engineered creature from another planet who just happens to look like an earth raccoon, and he has kind of a Brooklyn-ese way of speaking. He’s also clearly the leader of the group and the one who hatches the escape plan to get the group off The Kyln. And he gets little help from his compatriots who nearly manage to screw it all up, but all of the character elements and Gunn’s direction make this scene work like a charm.

The rest of the preview was basically an extended trailer giving us very quick glimpses of other characters including Lee Pace’s Ronan the Accuser, Benico Del Toro’s The Collector (introduced at the end of Thor: The Dark World), John C. Reilly’s Rhomann Dey, and Thanos … well, his arms. I supose they still want to keep Thanos under wraps, but if you’re going to hold a special preview for the die hard fans, you might want to give them just a little more Thanos. A minor quibble, however.

The preview was introduced by Gunn, explaining that the film had been reformatted for the IMAX presentation (it’s also been post-converted to 3D), and it looked stunning. No surprise. The image was sharp and colorful, and even the 3D was pretty immersive. This is definitely one film that looks like it will be worth the couple of extra bucks to spring for the full IMAX presentation. Marvel might be a little worried by audience unfamiliarity with the characters (and may be sweating bullets over the failure of the summer’s other original sci-fi action film Edge of Tomorrow), but after seeing the preview — and being totally unfamiliar with the characters myself — it’s safe to say they have nothing to worry about.

Guardians of the Galaxy promises to be the summer’s biggest thrill ride.