I tried Mario Strikers the other day, and I must say, it was a lot more fun than I had expected. I haven't tried the online mode (in fear of getting completely owned) but I see a lot of potential for fun if I invited a few friends over. of course, they'd need to bring their own set of controllers since I only have enough for 2 people. I played this game with one of my friends and it was pretty intense. I've heard good things about Mario party 8 as well, although I haven't tried it yet.
Go rent it and see for yourself if you're not sure.