I think it's probably the best one I never played, at any rate. "Gimmick" - or "Mr. Gimmick", as it was going to be known in the U.S. release that didn't happen - was made by Sunsoft, and came out in Japan in 1992 (Sunsoft also did the NES Batman and Blaster Master games, for some context). I had never even heard of the game until this week, but luckily, Frank Cifaldi over on the 1Up Retronauts Blog saw fit to change that with a very well annotated video walkthrough of the game.
It's remarkably impressive. In terms of visuals and audio, Gimmick stands comfortably above almost all of its contemporaries, partly thanks to special hardware manufactured into the cartridge. Its gameplay is 100% classic platformer, with a lot of extra touches [enemies with personality, remarkably consistent physics, brain teasing secret areas] that we usually only associate with first-party titles on Nintendo systems, and sometimes not even then. Had it been released stateside with some marketing support, I can't help but think it would've been a hit.
Sadly, of course, that didn't happen, but I'm glad at least that thanks to the internet this little gem hasn't been entirely lost. I've embedded Part 1 of the video walkthrough below, and the other 3 parts can be watched on YouTube by clicking the links that appear at the end of each segment. Spending a half hour watching somebody else play a 20-year old game might not sound very thrilling, but if you're at all interested in the history of game design, give it a shot. I suspect you'll be impressed.