My personal rating system:
1 star – painfully bad, probably didn’t even finish it.
1.5 stars – just plain bad.
2 stars – good ideas that were wasted or weren’t enough to save it.
2.5 stars – one or two things saved it from being completely terrible, but only just.
3 stars – mostly good, but one or two things that annoyed me/just ok.
3.5 stars – pretty good/great ideas mostly done justice to.
4 stars – very good, loved it with only one or two problems or boring bits.
4.5 stars – nearly perfect, any problems are noted but able to ignore them.
5 stars – amazing, a new favourite.