I know what you are thinking. Monsters Vs. Aliens is just a movie tie in, and for a movie targeted at young kids, at that! Movie tie ins don't exactly have a good record, as far as good video games are concerned. There are a few exceptions to this trend lately, like Kung Fu Panda. Monsters Vs. Aliens is another exception, with interesting characters, a fun style, different gameplay elements, and co-op on top of it all.
The title pretty much gives you all you need to know about the plot. We've not seen the movie yet, but the game, at least, introduces the monsters and pits them against the aliens pretty quickly. The monsters are all based on classic movies. You have Ginormica, a normal woman who grew to enormous height. The Missing Link, a hybrid monkey/fish, is a throwback to the Creature from the Black Lagoon. B.O.B. is a blue glob of goo. Dr. Cockroach is a mad scientist with the head of an insect. Insectosaurus, a colossal caterpillar, rounds out the group.
To my son's disappointment, you cannot play as Insectosaurus. More's the pity. The rest of the monsters are all playable at some point. You can't choose which monster to use for each level, which would normally be a bad thing. However, the levels are totally tied to the monsters abilities, so I can see why the developers went this way. I'd rather see well conceived levels, unique for each monster like this, than generic levels suitable for any monster. Kudos to the developers.
Ginormica is the first monster the player gets to use. Her abilities are mainly tied to her mode of transportation: she steps on a pair of jeeps, and uses them as roller skates. The skates allow her to zoom around quite nimbly for a woman the size of a large building. Ginormica's levels reminded me of a racing game, for the most part, with a few heavy doses of Tony Hawk thrown in for good measure. Ginormica can grind on the walls, jump and duck to avoid obstacles, and when that doesn't work, she can punch her way through them.
The Missing Link is the closest this game has to a typical action style character. He is strong, acrobatic, and has great one-liners to liven things up. In addition to punching, kicking, and jumping moves, the fish monkey can spin on bars and literally bounce around like a pinball in certain sections. Quick time events are used often for The Missing Link. Unscrewing giant bolts to disarm huge cannons was particularly fun, rotating the left stick like crazy. The Missing Link even has a Matrix-esque cannonball attack, which has to be seen to be truly appreciated.