Here is a simple template edit that will allow you to put comments on your game page.
First, go to disqus.com and register an account, add your site, etc. It will tell you what to do. Get the embed code, from the install page.
Second: go to to templates -> arcade_play
Third: find the second </div> and paste the embed code under it.
If you want to add facebook comments, I'm sure you all know how to get the embed code. Just do the same thing.
There you go!
If your wondering if: you post a comment on one game, then will it show up on the other games? No it won't. Each comment will stay on the page it was commented on.