Last week I won a Wii at a party. I finally got a chance to use yesterday for the first time, and it was fun! The controller takes a little getting used to, but I can certainly see why it's so popular.
There's a bowling game that we had a lot of fun with at a party recently. I'm not sure if its a standalone game or if it comes with many other games on one disc when you buy the Wii. At any rate, if you plan on having people over I highly recommend some competitive games like bowling, tennis, etc. The Wii is the best system out there for that kind of fun. I haven't been too impressed with 2player games on other systems, Xbox360 and PS3 have a lot of big title RPG's and action games, and they're interesting, but at parties or with friends the colourful and fun games of Nintendo are better IMHO.
I'm sorry, I didn't mean to mislead you; I don't have any of the games that I mentioned earlier, but they were highly recommended to me. The only game I currently have is "Hajimete no Wii," which came with the spare controller that I bought.
I agree that the Wii is great for multi-player games. Nintendo has always been more cheerful than the other consoles, and the Wii is no exception (although in honesty I haven't actually played any of the other ones. The last console that I actually bought was a PS2, and I only bought a handful of games for it. I almost never used it, so I had decided not to buy another console again. Good thing, too, or I might be stuck with two Wiis! )
I have a Wii at the inlaws, I love Mario Smash brothers and Wii sports. I also have Olympics, which is a level up from Wii sports if you ask me, Mario party (not that special), and Wii fit which is really fun (especially the balance games).
I am looking forward to buy the new soccer game...
You two would love "Super Mario Galaxy." The cooperative element is quite fun. "Metroid Prime 3" ... I'm not so sure that you'd like the "Aliens"-style single-player exploration. You should definitely look into "Mario Kart Wii" (online capable, hint hint!) which is coming out soon. I'll let you know if I think of anything else.
Update: I would, of course, be failing in my post were I not to recommend "Super Smash Bros. X" ("Super Smash Bros. Brawl" in the west). That there is great multiplayer action (and even international online action, hint hint hint). But I wonder with Lady Mikawa would go for it.