I own MadWorld and it's not all it's cracked up to be. It's okay, but it's short, niche, and frankly, kind of dull. The humor is top-notch and the gameplay has it's moments, but overall I find it hard to justify my first-day purchase.
The Conduit I haven't really played much despite buying it first day (because I'm weird that way), but I enjoyed the parts I played and from what I've experienced so far I think it should've sold more.
Silent Hill looks great, but you can't expect a classic horror game like that to sell millions right away.
As for Dead Space Extraction, I think it looks like a well-made game but not my type of game. Which is probably something everyone agrees with.
See, rail shooters are already oversaturated as hell on the Wii. RE-rail shooters sell because they are RE. People love RE. Same reason Mario sports-games sell, they're not bad games, but people buy it because they love the characters and the brand name makes sure you'll get drawn in.
House of the Dead is the same, except it's smaller than RE. Add to that that everyone seems to love Overkill to death, I've heard tons of good feedback about pretty much every part of that game except maybe the length.
The only thing I've heard about Extraction is that it apparently has game-breaking bugs. So yeah.
EDIT: If you want quality core games from 3rd parties on Wii (Why people want to always limit it to 3rd party games I will never understand), check out No More Heroes. Amazing game. Resident Evil 4 - Even more amazing game. It doesn't matter that it was on GC and PS2, the Wii controls make it even more sensational than it already was. Still not satisfied? Try out Okami.
All the games you listed are, quite frankly, pretty average.
