I use FireAlpaca. It is pretty nice as far as programs go. It isn't going to offer everything photoshop does, but no one uses 90% of photoshop anyways. (Seriously, I got to be instructed by a pretty amazing animator who uses photoshop a lot, even he doesn't know what half that shit does)
The brushes are a bit weird but you can download brushes other people make as well as make your own. So far as I can tell is has virtually no layer cap which is very nice since I tend to work on roughly 15 layers in one project. I haven't run into any issues with my tablet and it either. Overall a very solid program that offers just about anything a general 2D artist needs. The only thing about it that bugs me is that there are some pretty basic brushes missing but you can find them online really easily.
On top of that the whole thing is free, which is really sweet.
I am not a massive artist and I have by no means stressed the limits of the program, but it has served me well. Plus it is free so there is nothing to be lost by trying it.