Android is powerful and technologically able to be the next big gaming platform, but unfortunately it remains too fragmented.
When someone writes a Nintendo 3DS game for example they have to develop the game and then test/QA it against a very small selection of systems (four or five).
When someone does the same thing on Android they have to test it against several thousand devices, and if they miss any one device people will leave negative reviews and it might sink the whole project (see every EA game on Android ever).
Plus, Android as a gaming device has some control issues to overcome. There are only certain kind of games that work well using on-screen controls and even if a sub-set of the market has a physical controller you cannot presume that in the design.
Essentially the only way "Android" could become a good gaming platform is with a massive lock-down. You'd have to develop a device, with its own market, and physical controls. Then lock out every app that isn't working within that strict ecosystem. Kind of like the "Valve Box."
But once you do that it isn't really the "Android" ecosystem any more, since instead you have now developed your own ecosystem with certain assured characteristics (e.g. hardware power, 3D support, physical controllers, etc).
http://www.pocketgamer.co.uk/feature.asp?t=how_to&c=4522...
which apple seems to be fighting, even preventing iOS specific controllers if they're not tied to specifc apps:
http://kotaku.com/5947934/the-first-apple+approved-ipad-ipho...
The controller market is a little bit, ahem, fragmented, but generally seems to be converging on the PS3 style since it allows the double analogue sticks to operate pinch, zoom, rotate and other two finger gestures. Compare Archos tablet with gaming controls, their tv-box with gaming controls, and the new Nvidia portable console:
http://www.archos.com/img/products/gamepad/dwd/Ambience-corn...
http://media.begeek.fr/2013/01/ARCHOS_TV_Connect_TV_touch_re...
http://i0.wp.com/hypebeast.com/image/2013/01/nvidia-unveils-...
Though interestingly Nyko only just released a couple of handsets build for Nvidia chips and in collaboration with Nvidia that use the XBox 360 layout of having the dpad as a secondary to the analogue.