1. The entire Half-Life series
2. The Elder Scrolls V: Skyrim
3. Far Cry 4 or the entire Portals series
Half-Life... Need I really explain? Sure, the graphics for the first one was a little cheesy, but who cares? The plot line, the creativity, and the graphics later on, not to mention you don't need much to run these games. It was fan-tas-tic.
Skyrim was the best medieval roleplay quest game I've ever experienced. The quests were awesome, so were the plot lines, and with a few mods, the graphics can be upped to that of a 2015 game (like Far Cry 4). Just amazing! :)
Far Cry 4. The plot, graphics, storyline, characters--just like Half-Life, it was amazing.
Portal; the puzzles were great, along with graphics, and I have a certain fondness for games concerning physics and are sometimes intellectually challenging to solve. Loved the series, the characters were nice.