The comments about the Addams Family and Zool definitely hit the mark for me. Addams Family was a really neat platformer, well designed, fun to play, challenging without being outrageously un-completable. I really loved all the hidden secrets, too! Right down to the Continue screen! I found loads of them, but I doubt I came close to finding them all.
As for Zool, I genuinely did enjoy playing it, but it got so much hype at the time, heralded as a Sonic-beater when it was nothing of the sort. It was a fairly entertaining and very colourful platformer, but held very little interest beyond that.
Oh, and whoever dissed Frontier, wash your mouth out!... OK, to be fair, Frontier's biggest blessing and curse was its open-endedness. You could travel anywhere in the galaxy and do any of the myriad of jobs on offer, but you'd always eventually get to that point where you'd done everything and you still hadn't "won" yet. I personally loved Frontier, I spent the whole of 1993 playing it, but I can see why it might not be everyone's cup of tea.