First a very important point that can be a bad one but it's how karaoke are made :
- no video clip and not the real singer / music (can be a bad point for some but "old school" Karaoke is the most fun while you sing on remade songs... and manage to make the song sound even less good when you sing lol)
So here are my wife's impressions (she was only ok to make a pros / cons list for me so...) :
+ huge song list
+ real karaoke software feeling (interface, settings...)
+ very fun when playing with more than 2-3 people (while Singstar can be long or inadapted to song sessions with a group of 5+ people)
+ price is well ajusted
+ some modes are quite interesting to try
- sometimes it sounds really cheap (like real karaoke lol)
- no french and no japanese songs for now
- most big license won't come here :
disney for example (or is it something that we can have one day?)
So for her, if you like a very specific genre of music Singstar styles games are better because you choose certain tracks that you can keep and play when you want (even with no online).
If you're a fan of Karaoke and you don't really care not to see your favorite star (or even hear her / his voice) then it's pure fun for like "hundred of years" !