When you turn on/reboot your phone you boot into multi boot where you choose wich OS to boot. It's shown with numbers and the kernels. So 1. woud be maemo and 2. would be NITdroid (if you're oc'ing you'll have 3 options, a power kernel aswell).

If you're in NITdroid and want to go back to maemo just reboot and then in multi boot choose option 1. (maemo). (remember to slide keyboard open when rebooting).

I've tried 3 games and they look and runs smooth, but they're made for multitouch, but some of them have keyboard choise (set as touchscreen). I'm not sure wich ones will work with keybaord. The ones i've tried are all 'try and by' from Gameloft