Oddly enough, even after all this time the App Store is still lacking a really solid Pokemon-like. There are a few out there that I'd describe as OK, or sort of similar, but if you're looking to scratch that collecting and battling monsters itch that you can only get on Nintendo platforms, there's not much out there. Or, not much before we saw Mirror Match Games' My! My! Monsters.
The game is in a very rough (and early) state right now, but I like everything they told me that they've got planned. They're trying to capture the essence of those nostalgic Pokemon games with all the exploration, collecting, and fighting that you expect but also with a hip social spin to enable all sorts of online community interaction.
The world map is delightfully pixel-y, and really fits in with the whole nostalgic theme they're going for:
As mentioned, the game is in a very early stage right now so it's hard to get into specifics when it comes to how large the world is going to be, how many monsters there will be to collect, and all the other social features. Mirror Match assured me they're really anxious to hear community feedback, so if there's some important features you want to see in a Pokemon-like, drop 'em in the comments.
My! My! Monsters Upcoming AppWatch Button Watch App