The ONLY way to game in a virtual environment is utilizing pass through technology. I got it working once, but due to my distro hopping ways, I scrapped the whole thing in favor of running the machine with XBox10 (Windows 10). I've since set the PC aside because I barely game anymore.
You really need a second gen i5 or better to do this, and a second graphics card will be helpful. 4GBs of RAM is NOT enough, you need at LEAST 8GB to game virtually. I used Virtual Machine Manager, straight out of Ubuntu's software center. I remember there was a few things that had to be tweaked, but I've since forgotten.
The thing I remember most, though, is that after all that work, it really wasn't even worth the trouble. After all, you're still running Windows. I say save yourself the trouble and headache, and make yourself an "XBox" for those games you can't be without, and have a dedicated Linux machine for real computer use.
Now aside from gaming, Virtual Machines are AMAZING tools for that certain software you just can't get running properly in WINE. Shoot, I even had a rig setup with several virtual machines running Halo PC servers and one Clan Forum.