This recording is, without question, not the best Grease Cast Recording available. I would recommend getting the Original Broadway Cast Recording (see my review on that one), especially given its price tag!
As far as this one goes, the singing is mediocre. That's why I buy a Cast CD ... for the singing. If the singing isn't up to scratch, I'm not happy. This recording does include some of the movie tracks ("Grease", "You're The One That I Want") but that does not make it a worthwhile purchase.
If you are a die-hard Grease fan (as I am), it's worth checking out to hear the variation of the material. Otherwise, just get the OBC recording and be happy.