First of all: Thank you for a great Facebook game that does not require you to constantly annoy all of your friends for leveling up and offers premium items for a fair price. (*cough* Zynga *cough*)

The only ting that bothers me a bit is that you can pay for victories – kind of. Some players use expensive weapons excessively, which requires you to do the same if you want to compete with them. Those who temporarily ran out of coins/credits are doomed to lose. Although I understand that this is partially intended to make people buy more cash/credits, which is how the game finances itself (and although it's a lot of fun to dominate people with superior weapons :D), sometimes you just want a fair match where both players start with the same weapons. It's really annoying to run into players with loads of holy grenades when you just ran out of ammo (but have some reinforcements left for another battle).

Therefore I'd suggest some kind of "Classic Battle Mode", which disallows the most powerful/expensive weapons. A simple checkbox you can click before searching for an opponent or challenging a friend would be awesome. I hope that makes some sense and that you consider my suggestion.