Scorpius is excellent, but hard as balls. Recommended for those who find R-Type too easy.
Goddess Blazon is a rather "meh" doujin fighter. Graphics look very PCE-ish though.
Ajax was a great port for it's time, but since he's emulating, may as well stick to the arcade version.
Angel Dive is wonderful, but not so n00b friendly as you have to HDD install it, and music is MIDI only, no FM.
Code Zero is all about the music, love it.
177 does exist on X68K, but it's actually a doujin port of the X1 version, not official. Same goes for Laydock, which is actually a port of the obscure as hell SuperMZ version. There is even a doujin port of Yosaku, the best game on the original Cassette Vision.
In general, the X68000 is just an excellent machine for making things more badass.
For example, Missile Command Special Version:
Regarding the Amiha, the X68K port of Lemmings retains the weirdo 2 player split-screen option with dual mice support. Yay.