Should be as good as the others with regards to online. Nintendo have always been good at online stuff but the problems have been that 1. they always required some sort of add on and 2. not many people played on line (see 1). The online stuff on the DS is fine so no reason to believe ti would be any different on the Wii.
As with the DS the Wii internet stuff will be built in (including WiFi).
With regards to the graphics, they will be better than the PS2 but not up to the level of XBox 360 or PS3 mainly because of a lack of support for HD, having said that with the exception of Gears of War I haven't been blown away by anything I have played on the 360.
Call of Duty 3 will be available on the release day, I'm not sure how the control system will work out but it looks like it could be fun to me.
http://www.game.co.uk/ViewProduct.aspx?cat=114 43&mid=329584