My Take
There are lots of great math games but my experience is that students choose games that are more a game experience than a math experience. Many choose to play the Run game, they control a player that runs on blocks, or Bloon's Tower Defense, students watch balloons pop, rather than other great math games that would increase their math skills and knowledge.
How I Use It
Only as reward/free choice time. The students don't often choose the more challenging games and opt for the goofier, flashier, noisier games unless prompted to do so.