One of the fun parts of Ubuntu is that its easy to play old Nintendo NES games. The photos above and below are just a few faves. Kung Fu, Mike Tyson's Punch Out, Hogans Alley, RC Pro Am, Duck Hunt, Tennis, Joust, Dig Dug, Russ'n Attack, Gauntlet and on and on.
So if you want to have fun right now, go up to "Applications > Ubuntu Software Center" and do a search on "gfceu" and install the GFCE Ultra NES Emulator (should be the first program listed).
Once the program is installed, you can find it listed under "Applications > Games". GFCEU's main menu has some tabs for making changes like enabling sound or going full screen. It also requires you to locate a game rom file... in this case NES files. I also recommend clicking the "Input" tab and configuring gamepad #1 (and or #2 if you have friends who also want to play). When you click onto Gamepad 1, it will pop up a little window for you to input you button. You'll have to press your buttons twice to confirm each keyboard button. A and B, Select, Start, up, down, left, right. If you dont do this you wont have any clue which buttons control the games. GFCEU even works great with a wireless game controller :) and if you are really serious, there are NES gamepads converted to USB all over ebay for sale.
So are you ready to play?
Check out some of the NES rom files at the link below. If that link doesnt have what you are looking for just search around the net for nes files like this "kung fu nes" or maybe "super mario nes". You're looking for .NES files.