Cutie Q (1979) - although only playable in the Japanese version, its code can be found on the American release.
Super Pac-Man (1982) - not in the Japanese version
Xevious (1982)
Mappy (1983)
Gaplus (1984) - the Galaga sequel
Grobda (1984) - a Xevious "spinoff"
Dragon Buster (1985)
Anyway I think Mappy is the most fun, in this retro collection, while Xevious is the most challenging.