Although Darkstakers may be light on the game-modes, it certainly makes up for it with superb action.
Unfortunately, the only letdown to this version of Darkstalkers for the PSP is that there are a very limited amount of modes to select. You have arcade, network, tower and training... that's about it. However, each mode is very fun, especially the 'tower' mode which proves to hold a challenge as you progress further and further to the top. Arcade is pretty much what you'd expect, you fight a bunch of opponents in a row until you reach the final opponent. If you succeed the arcade mode, you're rewarded with an ending movie for each specific character. And finally, network is the mode to challenge your friends who also happen to own Darkstalkers. It's very fun as multiplayer fighting games always tend to be, and there's quite a few options to tweak to your liking, such as setting to 'punches only' or 'kicks only' or just completely disabling special attacks.
There are 18 characters to select including the legendary Morrigan and cat-woman, Felicia. Each character, of course, has their own unique set of moves, so you can always check them out in the training mode to see which character is right for you.
If you're looking for something a little different to Street Fighter but along the same lines, Darkstalkers is what you've been looking for. Despite it's few gameplay modes, it certainly makes up for it.