I'm not at all comparing this to the MAME CRT Arcade Monitor experience which I also have and love.. but recently got a Samsung Galaxy s4 and tried MAME4Droid on it. Have to say I'm surprised how good the games looked on the small screen and the fact that the older games run silky smooth on it. I didn't know that AMOLED screens have basically ZERO lag at .01 ms of response time.. that's 1/100,000th of a second! Technically faster than CRT response time even though your eyes cannot tell the difference. Another plus is that unlike LCD screens, AMOLED does not use a backlight but the pixels themselves provide the light. So you can get perfect dark blacks that make backgrounds in games like Mortal Kombat looks amazing. IMO it makes MAME games feel more like your playing on a CRT with the Scanline filter activated. The only thing is that AMOLED technology at this point doesn't have the most accurate colors, very vivid but a bit oversaturated and cartoony looking compared to a CRT. However that is not really much of a downside because most arcade games are cartoony in the first place.
I'm sure AMOLED displays will be the future if they perfect the colors to make them look more realistic. I know this is not new news to anyone. And yeah touch screen controls suck unless you hookup a controller of some kind. But just for a decent visual MAME experience, this is not bad for MAME on the go. Does anyone think AMOLED screens will be the display of choice for MAME over LCDs, when CRTs are no longer around?