I don't think the dimension matters if a game is a good game. 2d, 3d, or 1d... whatever text adventures are considered... any one of them can snag in users and grow to be huge. Look at pretty much everything zynga absorbs. Not sure that was ever untrue per say. Just that it was safest to go with running trends, so games must have 3D marketed somewhere in there or publishers doubt the potential.
As we see the marketplace for apps grow larger with independent developers (and also much shittier since indies are also composed of half assers who vomit garbage into the app pool shamelessly) - we see that without the demands of publishers, the developers are free to create whatever they want. Many, like me, are only interested in 2D games. 3D can be ok but it's rare I give them a shot cause I like the era I grew up in. Super nintendo, genesis, master system, NES, etc. Those take me back. That's why I play games. Not because I want some alternate universe or anything. I don't like games trying to look as real as possible cause life is too real and I don't like life. So 2D is - and always has been - in for me. I know I'm not alone in that one.
Mass appeal, however, is another story. While there are always going to be those of us who would rather play metroid than medal of honor, we might be like the group of people who prefer midget amputee interracial tranny porn over the mainstream stuff. Who do you want to cater toward?