The 5-star system is not recommended for all cases. 

It has been discussed and covered in many UX and media websites and forums.

Maybe I'm biased, but most authors and buyer I know rate 5-star or none at all...and when someone receiveis anything short fo that, most of the times is 1-star and they feel attacked (and some times it is an attack).

Wouldn't be more beneficial to switch to a thumbs up/heart system?  If you like, mark you like it. Otherwise, don't.

Some studies say this increase the number of ratings too.

Anyway, just my 2 cents.