I got Karaoke Revolution Vol. 2 for Stephanie a couple weeks ago, though it feels more like one week ago considering how much time we've actually had to play it. The game monitors your voice and rates you based on whether you are on key and saying words at the right time.
It can't tell if you're singing the right word, only whether you're singing it at the right time, but anyone who's actually sung Karaoke will realize what a blessing in disguise this is--half of karaoke is stumbling over half-pronounced words in an effort to keep up with the song you thought you knew.
This brings me to my next point, which is that regardless of the whole "singing on key" that you're required to bring to the table, the key component to doing well is still, unsurprisingly, knowing the song. Being comfortable with the words to a song is key to your ability to sing it in a way that will match an existing version.
The game includes something like 35 songs. The selection is very decent and quite diverse. It's includes plenty that most people will recognize and even a few that you may love--it's got one of my personal karaoke favorites, Steve Miller Band's "The Joker," for instance. On the downside, you will run through the songs pretty quickly. However, it will take a bit more time to familiarize yourself with all the songs well enough to sing them well.
I just now rocked the fucking house with girly standards like "I Will Survive," "...Baby One More Time," and "Lady Marmalade," along with Good Charlotte's obnoxious, whiny teen-angst cash-in "Perfect." Again, sing what you know. I surprised myself with a halfway decent showing on "I Believe in a Thing Called Love," which I barely knew the last time we popped the game in. (Coincidentally, the day after that I heard the song on someone's ringtone. I think that call was for me and destiny was on the line.)
I also had fun with the chorus of some catchy country tune called "Friends in Low Places." The rest of the song was a disaster, but oh, that chorus! At the end the audience starts to join in, and I really felt like I'd delivered a rousing performance. I made an "everybody sing" gesture toward the television, reveling in the adulation. For that song it works better when you sing with a country twang.