I just built a RetroPie gaming system and have been focusing on MAME games. Here are my favorites so far.
I have over 5000 games loaded, from:
Sega Master System
There are probably 4700 I've never heard of. I'm going to try a few from this conversation.
I'm debating whether to build a cabinet and put in real arcade buttons, joysticks, trackballs, etc. Trying to see how much I actually play it first.