While I read Singstar is good, the thing lips has going for it is that you can plug in your zune or ipod and karaoke to any mp3 you have on it. So regardless of the songs that come with the game, you have thousands of songs available to you.
Of course, the lyrics don't come on screen (the game has some sort of music beat detecting stuff to assist what to show on screen), but that doesn't really matter when everyone has had a few drinks. If you have your tags correct you could print out the lyrics though. It's an extra step, but worth it to some if you want to sing any song you want.
Of course I prefer rb2, but the selection is limited, and the girls singing hate doing songs they don't know and/or are hard. Five hours of no doubt and weezer gets boring.