Thanks guys. By simple games, I meant PacMan, River Raid, etc which I think I can find all for MAME. I did play a bit more yesterday and got some games working under RetroPie. The bartop is now setup with some Atari 2600 and 7800 games. I have downloaded 0.78 MAME compatible ROMs but I had to put them into Atari folders under RetroPie (not under MAME folder). Kinda weird in my opinion but at least most of them are working.
There is a slight lag when entering options on RPi2 but the games run smoothly. RPi3 is only $35 so I may upgrade anyway.
As an alternative, is there an easy MAME only setup for Raspberry Pi? I am asking because, while I do not mind running RetroPie, it is setup to support many emulators and it looks like I am going to be running just MAME.