I missed Guardian Legend growing up and I tried it several years back as a ROM but I didn't have the patience for the top down maze parts. The concept was awesome but I remember getting lost or missing something, I'll blame it on some NES games being nebulous if you didn't have the instruction manual.
SMB2-3 really got me into platforming games though and *I* would say are the best. Is OP actually looking for hidden gems and not necessarily the best games though?