Unity isn't the best fit for 2D games anyway. Unfortunaty, there isn't much out there in terms of engines for 2D... Well, I take that back... There are many 2d engines out there, but most are libraries that you include in your own projects. There are only a couple good full-fledged engines (like unity) out there for 2d, most notably are GameMaker, MultiMedia Fusion, RPG Maker, and Torque 2D..
I'll look at each of them here:
1) GameMaker -- honestly havent heard many user stories in regards to this one, but I don't like that it uses a non-standard language. This means that I need to learn a new language that I will never use anywhere else.
2) MultiMedia Fusion (MMF) -- Great for begginners as it is entirely gui-based; no scripting at all HOWEVER because of this, it is relatively limited in terms of capabilites.
3) RPG Maker -- Well, first of all, it's restricted to only making RPGs (which happen to also be the most expensive games to make). While it has some scripting functionlaity, it's very crude, so there are some things that you simply can't do...
4) Torque 2D -- Great tool. the best on the list, except for one problem... It doesn't support Android... :/
Looking at this list, you can see that none of the options are really that great, which is why I am working on my own open source engine that will aim to fix this. With that said, it's a ways off.
