I had a think of the games I played a lot and made the most of the MTX hardware and came up with in no particular order:
Chamberoids
Highway Encounter
Downstream Danger
Sepulcri Scelerati
Surface Scanner
It's probably no surprise those are all later games and there's one convertion from elsewhere.
Chamberoids, because there wall always the thought that just maybe it could be done faster.
Highway encounter becase of both the looks and the fact it could be finished in a reasonable time.
Downstream Danger and Sepulcri were so damn hard, because they both needed pinpoint accuracy, but had the just one more go appeal.
Surface scanner had the one more go/get a better score appeal too.
Honourable mentions to Kilopede and Hawkwars amongst the earlier games for getting a lot of playing time while not being overly advanced.
Son of Pete got plenty of play time too, but my version was hacked for 99 lives, that made it much more playable that the un-patched version
