I just built a RetroPie gaming system and have been focusing on MAME games. Here are my favorites so far.

Asteroids
Centipede
Defender
Donkey Kong
Klax
Lode Runner
Missile Command
Qix
Tempest

I have over 5000 games loaded, from:
Sega 32X
Sega Master System
SG-1000
Super Nintendo
Atari 2600
Atari 7800
Game Gear
MAME games.

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.