Transformers Game: Consoles VS PSP VS DS

I was wondering how different the PSP version will be to the console versions? I know the PSP gets 20 playable characters (as opposed to 9 in the consoles), and also some sort of ad-hoc multiplayer, but is it essentially the same game (just expanded a bit) or a totally new game?
I sorta need to know since, not having any new console, if I want the real game, I'll have to buy the PSP version. And if it's worse for some reason, I could look into the DS version (which I KNOW is totally different). It just seems odd that they'd pack 11 more characters and some other add-ons into a handheld and withhold it from the consoles...it seems like I'm missing something.
I sorta need to know since, not having any new console, if I want the real game, I'll have to buy the PSP version. And if it's worse for some reason, I could look into the DS version (which I KNOW is totally different). It just seems odd that they'd pack 11 more characters and some other add-ons into a handheld and withhold it from the consoles...it seems like I'm missing something.