The significant thing that I didn't enjoy was the ridiculous amounts of plot armour on the characters. 90% of the battles just ended up being set-pieces because nothing actually happened during them; action happens, no one gets killed, everyone retreats, and at most a change that could have happened with just dialogue occurs. These people are fighting monsters in human-form. My understanding was that humans could not match the strength / speed / etc. of the servants, hence why the Masters summoned them to fight instead of just the doing it themselves. Yet Shirou repeatedly does just that (or at least enough to survive and be healed by Avalon). Yes, his magic gives him the ability to 'borrow' the skills of the weapon user he copies, but as shown later when fighting Archer, his magic wasn't nearly as good as the original. And no one stops him from even trying, despite that he has no actual chance.
Archer's "one goal" that he had basically continued to function solely for that purpose was to kill Shirou. What does he do? Beat him up once or twice, never doing any real damage despite many opportunities to finish the job. And then.
Caster could have wrecked Rin in a second during their battle, but what does she do? Continue to toy with her and gloat until Rin goes in for a melee kill, which I'll give a 50/50 to, as I'm not familiar enough with their powers to say whether or not Caster's actually that weak to plain super-punches, when Kuzuki basically did no damage to Saber even with Caster's far superior magic enhancing him.
Lancer's sent to finish the job and kill Shirou, what does he do? Slowly chase after him and play around with him until Saber gets summoned (though seeing more of Lancer's character later I must admit, I'm a bit more lenient on this one, but it's still ridiculous).
Rider has Shirou isolated and ready to be killed, but instead decides to play around with him, and then for some reason retreats when Rin shows up.
The only one I can forgive is Shirou vs. Gilgamesh, as it actually had a reasonable explanation; Gilgamesh is a stuck up fool and didn't take him seriously.
All the other masters / servants continuously hold back for no apparent reason.
I suppose going from the game to the anime just kind of has that effect though. In the game, you'll make 'wrong' descisions that end up with the character dead, and you have to change that next time. But the problem is that going to the anime, it must follow only the 'right' choices, having those situations add up again and again, making it just feel like plot armour.
Additionally, coming in from watching Fate/Zero, it started off a little slow with the slice-of-life / high-school drama kind of thing for me. Not to say that it was done poorly, it just wasn't what I was expecting or hoping for, and I must admit that it had a slightly negative impact on my opinion of the show.
8/10. Thoroughly enjoyable to watch, but too much bad to rise beyond an 8 for me. Will need to do a binge re-watch at some point to see if I want to change that.