I'm kind of on the fence with Monsters Ate My Metropolis. I loved, loved, loved Monsters Ate My Condo, didn't love Super Monsters Ate My Condo so much, and am not completely in love with Metropolis...
The game is very animated and zany and wacky and hilarious, just like the first two. The animations are top-notch and very over the top, which is a huge part of the series' charm and is what keeps you coming back for more! The new card matching battle system is, indeed, very fun and addicting, but I have a few problems with it...
1) It's increasingly clear early on that getting powerful cards is very difficult, due to the random nature of the card purchase system. This has put me at a severe disadvantage very early on, because people within the same rank as me with similar populations somehow have entire decks made with cards that deal no less than 240 damage, whereas my cards range from 55-309. This seems like a push to get people to spend money to get better cards, and I don't like that.
2) You earn tokens pretty slowly, in my opinion, and I can see this becoming a bigger issue once you level up more and don't get your energy meter refilled as quickly as the experience gap grows.
3) The energy meter, yuck. Don't like it. I also don't like the fact that you can only connect with friends through Facebook. I never, ever do that, so this puts me at a disadvantage.
Other than that, I really enjoy the game. Just all of the F2P trappings turn me off pretty severely, but I see this game doing quite well for itself once it releases to the public.
Edit: TWO THINGS I FORGOT!
1a) I wish one could swipe up on the cards to play them instead of having to tap the card to select it. By habit I keep swiping up before remembering to tap.
2a) There's a bug that happens whenever I have to tap ferociously. After I do it successfully (achieving an Awesome score), the animations speed up by double. The battle tap thing doesn't speed up, just the animations for the entire rest of the battle. It's a bit distracting.
Edit2: forgot one more thing: the Mega Zone attack is totally pointless. The damage output from it is absolutely worthless unless you have a crap hand. 9/10 times I was better off playing a card in my hand.