Fifa 18 despite getting great (mostly) reviews is getting the usual metacritic user review treatment - currently at 4.2 or something out of 10. Looking at the reviews you either have realistic scores like 8 or 9 but then a whole load of 1's and 0's.
Most of the poor reviews mention PES and so it is pretty obvious these are getting sabotaged by PES fans desperate to make fifa look bad so they get some people to consider moving over.
Fifa fans clearly don't reciprocate en masse with lame reviews on PES and so it has a relatively high score from all the PES fans going crazy.
I suppose the user scores shouldn't be taken as seriously as the critical reviews