Hmmm, I can't put my finger on it. There's something that makes me think you guys could be so much better!
I actually thought your singer was quite good, but the songs don't really flatter her style and timbre. Maybe try slowing the songs down? Everything seems a little rushed and breathless (the music that is, not the singer).
Also, I think the songs you have decided to cover are quite characterless too. Again, as others have mentioned, I know you need to try to cater for everyone by playing songs that everybody knows, but you really don't need to sell out as much as you think to keep customers happy. Try and pick a few songs that are dynamically and musically interesting. I'm sorry to say it, but you all looked a little bored. Covers are supposed to be fun!
It just sounds like an un-mastered CD. The music's there, it's tight and it's ok... just needs finesse!
Truckstop