I get a lot of mileage out of emu'd Neo Geo titles on my DC. Neo4All plays stuff fast and looks great (I think some of that has to do with the skill of the person doing the emu/conv so respect goes out to personal skillz also).
My interest with Neo Geo games is to have them on self-booting, single-game CDs that casually interested people can drop in and play without having to select things from menus. It also makes it easy to hand a pile of discs to a kid and let him "just play".
Anyway, it seems like some Neo titles were meant to be 2 player (Neo Drift Out, Neo Drift Out New Technology, etc) but they don't actually work with 2 players, while some games like Top Hunter and Metal Slug are good with 2 out of the box - is there a controller combination trick to enable 2 players?