This is mostly a platformer game. The story is - I don't really understand it myself but from what I've gathered slowly but surely, it seems like this alien called Malware is trying to suck some sort of morphic generator, as its called. This one guy is traveling through time (the guy's name is Rook) so he's switching between the future and the past, so this is why there are two Bens. The second basic premise is that it's all about the aliens. As you might know from the normal Ben 10 show, Ben has this thing on his wrist that allows him to change into aliens. Now, the thing about both of the Bens is that they can usually transform into the same aliens. I will name a few for you:
The thing about both Bens that's interesting is that they both have their own aliens that are unique only to them. For teenage Ben, he has Shocksquatch, Crashopper, and Gravattack. For younger Ben, he has Eyeguy, Feedback (a new alien), and XLR8. Also in this game, you can get upgrades that let you do certain things in the game that would let you do what you couldn't do before. One of the last upgrades allow you to change into all the aliens, letting teenage Ben have Eyeguy, Feedback, and XLR8 and younger Ben can also have Shocksquatch, Crashopper, and Gravattack. I recommend getting the upgrades as soon as possible because it can really be fun to use all the aliens with one Ben.
I would give this game a B because it's not the best game but it's pretty fun at first. It seems like it was easy to beat in no time at all.
Here's a tip for the final boss: Malware will do an attack. You should dodge it and then his shield will go down and then you attack. Eventually you'll have to fight two Malwares at once.