When I first got into GroovyMAME, I soon discovered the limits of my Loewe CT1170. Amazing picture quality (thanks to the E3000 chassis) but the circuitry only accepts a narrow range of video modes. Basically, anything that moves away from 50 or 60 Hz creates image distortions and, at 60 Hz, the TV won't display modes with more than 224 lines. That's pretty frustrating since so many games in MAME have 240 vertical lines!
When I tested out a Siemens for the first time I was pretty blown away when I saw R-Type running with 256 lines correctly displayed!
The search continues...