Yes, there is offline multiplayer. You can connect up to four controllers, but multiplayer games like Wario only require one controller for up to sixteen players (you pass it around).
As for Gamecube controllers, there are slots on the top of the system allotting for two controllers and two memory cards.
You can download "virtual console" games off the internet via the system itself. You can pay for these by credit card or purchase Wii points cards in increments of 2000 points. Most of the VC games cost between 500 and 1000 points each, I believe.
The games come in regular-sized discs, unlike the gamecube discs.
I would say the Wii is a great system if you are looking for multiplayer or family oriented games. Of course, there are a few good single-player games available for it, but for me it just wasn't convincing enough to keep the system. It still has a lot of very cool features, however, and very innovative gameplay.
I would definitely reccommend it if you have wireless internet, and if you have family or friends to share it with, and, of course, if you are a fan of Nintendo's classics.
Hope this helped.
