You may have played Z2Live's first big freemium iOS game, Trade Nations, and the recently released Battle Nations is a sort of spiritual sequel to that one. It features the same kind of Farmville-style gameplay, so if that turns you off, you should probably just go ahead and move on (Happy Thanksgiving!). But I do have a place in my life for about one of these games at a time, and Battle Nations is a really well-done version of this kind of game, complete with a pretty interesting turn-based combat twist.
The idea is that you're running a growing encampment of soldiers in an empire, so you need to first lay out housing and workplaces for the soldiers, and then work to make your technology better and your army bigger. The core loop of the game is earning gold and XP with farms and businesses, and then you use those resources to make your troops, which can then carry out missions and win fights for you. There's a single-player "storyline" to play through (though you can't really "lose" fights -- you just try again until you win), and then the game is also very social, so you can start fights with friends, or give them some counterattack help if they're getting attacked by someone else.
Battle Nations has pretty much everything you want in a casual game like this -- solid graphics and sound, and a pretty strong backbone (though loading up the game when it starts can be slow, and unfortunately Z2Live uses their own sign in service rather than Game Center, which doesn't help). My one problem with the game is that it's a little slow: There's a long tutorial sequence in which you're taught how everything works, and your various tools and mechanics unlock as you level up. I also hope that there's a market system like the one in Trade Nations that allows for trading and selling resources between friends, but if there is a market to unlock, I haven't gotten there yet.
Still, for the low, low price of free, Battle Nations is a solid freemium empire building game that will keep you coming back at least as long as it takes to build up your camp to where you want it. It's free on the App Store, in a universal version, right now.