Well I've bought many Wii Games (currently I have 21). Major Letdowns IMO:

Need For Speed Carbon: Terrible controls (up to the scary point).

Brunswick Pro Bowling: I actually had more fun with Wii Sports' Bowling. (Only me could possibly buy this).

Minor Letdowns:

The Bigs: Personally, I ain't a fan of Beisball, and starting with a complicated game didn't helped.

Marios Strikers Charged: Big fan of soccer... but that ain't soccer. I'll wait for PES or FIFA 08

Mario Party 8: I don't think i have to explain why (do I?).

Medal Of Honor Vanguard: Simply worst than any of its predecessors.

I think the glove thing with sensor should be the next target IMO. I once worked on making something like that to control a robotic hand and it was fun. It ain't that complex and it's easy to use. Maybe just 1 glove and 1 wiimote or something. Also the voice commands is probably another field where they can develop (nintendo has already tried that a couple of times). And of course, it will likely to have better graphics, but up to what extent, Wii don't know.

About a Smell device: those things are expensive and would require recharging (as it uses different sustances to create a similar smell to the one you want). And i'll likely turn it off while playing manhunt.

fudg_er: warioware rocks, and it last more than an hour (the idea is for you to unlock all mini-games, not just to beat each level once). So far, I admit it ain't as good as Zelda, but i have more fun with it than any other games.

 Taz720: You will miss it, its not the game that makes the wii great, but the control it has. I ain't a fan of zelda, but its 10 times better than most games from the other 2 consoles (Xbox 360 and PS3).