gumby, I think there are a lot of great WiiWare games, but most of them I would not consider "hidden gems", they are more the high profile titles. If you are interested just in WiiWare in general I'll go over all the games I have.
For recommended WiiWare games in general I own and recommend: LostWinds (1 and 2, my two favorite WiiWare games), Art of Balance, Flowerworks, Megaman 9 10, ExciteBike World Rally, Airport Mania, Rage of the Gladiator, Cave Story, NyxQuest. These are all really great games.
Other games I enjoyed but would be slower to recommend: Swords and Soldiers (fun, but eventually you just press the same button over and over), Sonic 4 (fun but too expensive), Strong Bad (fun if you like the website, but too expensive), Dive: Secret of Mendes (Fun, gets a little repetitive), Water Warfare (almost good enough to recommend, but if you are picky about FPS controls don't get this game), TV Show King (Fun if you like trivia and have people to play with, but get the sequel its cheaper and has online).
Did not enjoy: Final Fantasy Dark Lord, Frogger (fun, but can find a free flash version just as good), Bomberman Blast (most people like this, but I just never figured it out).