Ars has an article about the difficulty of making games for the Apple Watch
Honestly, I think games are a bit of a stretch. Maybe I'm just a stupid old man, but I kind of feel like smart-watches should do very little, but everything they do, they should do in a simple, obvious, transparent manner. If you want to play games, just pull out your phone.
Now of course someone is going to say, "What's wrong with extra functionality? If you don't want it, just don't use it." All I would say is, if I had my say in the design, I'd make the UI as simple as possible, and make the battery last as long as possible. Adding a bunch of unnecessary features and games that require a bunch of processing power are likely to run contrary to both of those goals. If you gave me the choice of being able to play Angry Birds on my watch, or shaving off a couple of ounces while extending battery life for 5 hours, I'd definitely choose the latter.