Grease is a classic musical with sing-along songs that everyone knows. I'm not a mad fan of it myself and I wouldn't go out of my way to watch it, but it's endurable.
Grease 2 should should never have been made for the simple reason being that it's utter rubbish.
The 3 stars I have given are for Grease, Grease 2 can have the 2 blank ones because that's about all it's worth.