For innovation:
1 star if there is no game. I use 1 as 0 since there is no 0 in itchio ratings.
2 star if it is just nothing but a simple platformer for example.
3 star if game is trying to do something even if it fails on it.
4 star if it is doing that different part well.
5 star if it is something I have never seen or unique enough even if it has done before.
The important part is being consistent on your rating.
For example if a game has no sound and music and you give it 1 now even the most basic game that has a sound effect should get 2.
Also don't sweat on it too much. We all going to vote even if you make a mistake if a game deserves it people will vote to the median place.