It's good, but bleak. Season 1 had made it clear that the deathmatch was being played for keeps, but... yeesh. What they do to Shirou's ideals and dreams is horrible. Admittedly the epilogue (i.e. all of ep.25) backpedals on that to some extent, but even after that it's still bleak enough to be no fun at all.
I still think it's a good show, but that final run of episodes isn't as high as the earlier ones on simple entertainment value.
We learn who people are, which in some cases is a surprise. The show doesn't spoon-feed you, though. If you want to know more about the mythical originals, you'll have to read up on them for yourself. You'll learn a name. You won't usually learn much about what this famous hero did in life, if indeed they really existed. (Fictional heroes can be reincarnated as Servants too in the Fate/stay night universe.) These tend to be solid, stirring portrayals that do full justice to the originals' heroic status... or alternatively their ability to be backstabbing killers and traitors. You wouldn't want Servants like these. Just ask Caster's first master, although you'd need to time-travel back to before she killed him.
Ilya is great. Yes, I know, I was always going to say that, but she is. The horror of her backstory explains everything and her relationship with Berserker ends up being heartwarming. (In a blood-drenched way.) Rin and Shirou can be funny. Caster gets scary backstory too. People like Lancer and Archer are about as safe and trustworthy as a rattlesnake with a hangover.
I wasn't that keen on Gilgamesh, though. I know he's hugely popular from Fate/Zero, but he just didn't seem that interesting here. He doesn't have any of the depth of the other characters. He's malevolent, smug and so powerful that he's a threat to everyone. That's about it, really, which is a problem for the episodes where he's the main threat.
The heart of the show, though, is what it's doing with Shirou. In hindsight, it makes sense of everything. Everything that people had been saying to him, one or two story details I hadn't really registered... it's clever. "Hero of justice." "A world where no one gets hurt." He thinks he's a fake for believing in those things, which might seem a bit counter-intuitive, but then again the story's about to slice open his guts with those very ideals. Some people don't like this. They don't buy the argument and they've claimed that it loses coherence outside its original context of a video game where you can follow multiple routes. Personally I think the argument's a bit flimsy in itself, but that the story buys it all the necessary weight in blood and horror. Being a hero is normally wish-fulfilment. Here, no.
There's no sex, by the way, despite being based on what's technically an eroge. You can see the scene where it was supposed to happen, but the anime finds a family-friendly way to play it. I'm not sure why "family friendly" was thought to be a consideration in a show where a child gets skewered on a sword, mind you.
Did I enjoy this series? For the first twenty episodes or so, yes, a lot. I particularly rate the two flashback episodes, incidentally, which do intriguing, ghastly things with Ilya and Caster. "Servants are just tools. What's on the insider doesn't matter." The last five episodes I respect, but they give me the chills. The production values are top-notch, to the extent that the show's been nicknamed "Unlimited Budget Works". I'm planning to watch more of this franchise (Fate/stay night, Fate/Zero, the Unlimited movie), but I hope they don't all go this dark. I like darkness, up to a point, but this... brrrr.