Well getting a system and a game simply because you're friends talk about them isn't a very good reason. Also you can get Halo 1 and Morrowind (Predecessor of Oblivion) on PC. They're both cheap, and personally I liked Morrowind better than Oblivion. Oblivion is far too restrictive, especially since it's a one player game. Spells, Enhancements, all greatly limited compared to the last one and the scaling system keeps you feeling weak throughout the entire game. Both are really cheap, and it'll give you at least a fundamental idea of eachs' gameplay, and whenever or not you'd be interested in there sequels.
I'm more inclined to buy a lot of games for systems you already own. I would make a few suggestions however, not sure what games you already own, so I'll just shoot. The Godfather: Blackhand Edition, recently got dropped to $30, perfect if you like GTA games, in fact the only GTA-eqse game I liked more would have been Vice City itself. Controls add a lot of sick pleasure to the experience.
Trauma Center: Second Opinion is excellent. It's like a dynamic twitch heavy puzzle game with anime overtones. I never played the DS version, Under the Knife, but I've told they're mostly the same game, so you can save a bit money of there. It also has a squeal coming out later this year for the Wii, Trauma Center: New Blood.
Excite Truck is my personal favorite Wii game. Loads of fun. If you wait it might get a price drop, all though I already think it's worth full price.
Ubisoft is also publishing Nitrobike later this year. A game made by the same team who made Excitebike 64. It seems to feature very similar gameplay to Excite Truck, and will feature online play.
You might also consider renting Madden. I normally don’t like sports games or football, but I loved Madden 07, and actually plan on buying Madden 08. Controls add a lot to the experience, and actually brought me back to when I played touch football after Karate.
On the upcoming port front, I’d check out Lego Star Wars. I’ve missed both games myself, despite a vested interest in both. This Christmas they’ll be the Complete Saga with includes both original Lego Star Wars and new Wii controls. You’ve also got Bully and Table Tennis from Rockstar.
On the more violent end of the spectrum you have No More Heroes and Manhunt 2. Hopefully one of which will get released this year. A reaction to Killer7, and a psychotic simulator with gruesome motion controlled executions.
You’ve also got Nintendo’s Big Three between now and the end of the year, and an online enabled Battalion Wars II and allegedly Wii Music is still on track for an 07 release.
From your current list, I’d make some further suggestions. I’d pass on Mario Party 8. I feel for a Party Game it just moves far too slow. You could consider WarioWare: Smooth Moves, or Rayman Raving Rabbids 2 later this year, which has a great focus on 4-player modes.
I haven’t played Monkey Ball, but I have seen some general disappointment from antidotal evidence. If you’re looking for a puzzle game, I’ve read Mercury Meltdown sounds like a challenging title, and $20 no less.
Another minor thing is I’d like to remind you that new 360 Games are $60USD, and Resident Evil 4 on the Wii is $30USD. Hope that’s at least somewhat helpful in your decision.
