I am rewriting this review after watching fate/stay night which I should have watched before this one.
Story - 7: Now, I think the fate zero seasons are better than fate/stay night. The background story is the same, magicians fighting each other using a summoned hero to obtain the holy grail, which would be used for either good or evil purposes. We see quite a few more adult characters involved in the holy war than in fate/stay night which makes us feel somebody actually cares about that war (I would say as opposed to fate/stay night). I still think the main story is not that original, the servants are more or less D&D archetypes, and the holy grail war is well... a holy war. That said, the story is quite consistent and flows very well, with a few surprises.
Art - 9: The artwork is very good and the animation is very decent. I have nothing bad to say about.
Sound - 7: Average, not really standing out and not getting in the way either.
Character - 8: I really like some of the characters in that series, the servants are archetypes, but well designed ones.
Enjoyment - 7: Sometimes the pace is a bit too slow (mainly a comment on season1, a lot more happen in season2), the fights are very entertaining. Some things are fairly predictable though.
Overall: I rate it 8/10 because it's actually better than fate/stay night and the very high artwork/animation quality. I think it misses originality to be up in the 9-10 range.