Even with lower graphics and limited selections of mature games, I have enjoyed the few FPS games I've played because of the controls. I'm a mouse type of guy and I never was able to learn to use mini-sticks in these games but the IR pointer of the Wiimote is just as natural.
I've played Red Steel (yes, the sword-fighting sucked but the game overall wasn't so bad as an FPS), Farcry, Call of Duty, Metroid... I also really like Force Unleashed (even if, again, sword control sucked). I'm expecting a lot from Red Steel 2 with Wii Montion+ (and I hope Force Unleashed 2 will do that as well).
Other than that, it's nice to have mini-play type games for party like Mario&Sonic @ the olympics, Raving Rabbits, Mario Party 8... Hours of fun watching each other making fouls of one-self, especially as you get drunk! I recommend the soda shaking game of Mario Party 8...
For accessories, at least 2 Wiimotes with Wii Motion+ and nunchuck, 1 classic controler add-on if you download the old games and 1 Wii balance board. That should be enough to start with. You can get Wii Play when you buy your second Wiimote, it's fun for young kids (and even the less young, sometimes