I find it's less tainting previous iterations and bring down the series average as a whole. That's just me.
I quite like most Final Fantasy games and tolerate others and hate a few. Those I hate don't make the ones I love any less loved, I might love them more even because I know what could have been done wrong to them. However those few I hate bring my whole opinion of the Final Fantasy series down, irrelevant of the greats I enjoy.