If you are not a fan of the TV series, you will hate this game.
Graphics: The human characters are just plain ugly. Their eyes are seriously trippy and the faces look nothing like the show. The aliens on the other hand, look simply amazing. The textures are great for a game based on a cartoon. Froom ripples to scales, these aliens are very detailed. Ben's alien forms actually look better in this game than in the cartoon series.
Sound: The music is terrible. The soundtrack sounds very cheap and hastily put together. The voice acting is great. The main cast is voiced by the voice actors from the current series. Alien force has a great voice cast compared to other cartoon network series. Those who watch the show may have realized that the main villain's voice actor was recently replaced on the show by somebody who just doesn't sound the part. Well, the game uses the oringinal voice actor which was a good choice. The sound effects sound directly from the show which is good.
Controls: Movement is just plain cruel. Not much work was put into it. Everyone you play as is slow. The only thing I do like about the controls is how they fit the Omnitrix into it. Switching aliens and transforming feels very natural and can't be imitated by other console releases.
Overall: Only play this game if you are already a fan of the series. Those who are hoping to use this to get into it will instantly hate anything Ben 10 after playing. The story is great and truly blends both the original Ben !0 and the new Alien Force series with a return from a few characters that didn't make it into the new show (yet). Rent, don't buy.