It has some great additional features, is well maintained and updated, and I've never experienced any crashed or UI stutters/lag due to Nova. Nova has a free version with almost all the same features as the paid version, and no ads, so you can test it out.

-at the moment it is not possible to integrate with Google Now the way the Now launcher does. Although it looks like this is officially going to change (and one of the motivations behind this move)

-tastes in launchers vary widely from one person to the others. I have quickly uninstalled pretty much all of the launchers I have tried since they all tend to give bazillions of options instead of focusing on good defaults.

ADW launcher Beta 2 is pretty good as well, but i uninstalled it because of annoying advertisements and developer's reputation

Holo launcher is as light as you can get with enough functionality without installing Chinese spyware

other than that only Lightning launcher which cost a lot and not sure how is it better than Nova