I'm going to call 1994 the cut off for 'early' Neo Geo. So 1990-1993 titles considered. This covers SamSho 1, AOF1, World Heroes 1 and 2, and Fatal Fury 1, 2, and Special for early fighters which I think is fair, I personally was not into fighters for Neo Geo and the ones I did enjoy were 98-99 period so I'm not one to talk about those games.
Nam-1975 is still a great game. I personally never had any love for Mag Lord, however nothing on the Neo Geo really replaced it.
Baseball Stars 2 is definitely great, and shame on everyone for not mentioning it yet, League Bowling is simple fun too and I would always have a space for it in my imaginary collection although I would have to say calling it great is probably a stretch.
Cyber Lip is good, but kind of pointless to own with Metal Slug existing.
So yeah, not much there, although the early library was certainly more diverse than later years, but a lot of it isn't really worth remembering.