When news about this series was launched, I somewhat had mixed feelings; the original Fate/Stay Night was so horrible, I pity myself for watching it, while Fate/Zero was absolutely fantastic, plus Ufotable, responsible for Fate/Zero, were producing it.
That brings me to Fate/Stay Night UBW.
In short, I'd say that this series was absolutely stunning. I'm so glad it didn't turn out like the 2006 one.
Granted, the story was not as compelling as Fate/Zero. However, I was deeply surprised by the dark elements that were introduced. The 2006 one felt like a sad piece of shit, where viewers are supposed to feel sorry for Shiro throughout, for being the absolute dimwit he is. Rather than a hopeless romance that Stay Night (2006) was, UBW is more focused on progress and action sequences. UBW might not have an extremely good story line, but it is fairly entertaining, without the presence of any loopholes.
One word. Beautiful. Ufotable probably produces the most beautiful and amazingly stunning visuals I have ever seen to date. If Fate/Zero amazed me, this has managed to surpass even that in terms of animation.
Both opening soundtracks, especially Brave Shine, have found themselves cemented on my playlist. Sound effects, outstanding.
If this anime has even a small flaw, this might be it. Obviously, this was a HUGE step up from the 2006 version, but it did lack character depth. Characters like Kirei, Ilya and Saber could have added more to the show, and I would have preferred slightly more prominent roles (but then again, it might not have been that way in the visual novel). The apparent lack of a distinguished antagonist didn't help the cause. Kirei was the perfect antagonist in Fate/Zero, so I was expecting quite a lot from him in this as well (as this was supposed to be a direct sequel). Nevertheless, the annoying character of Tohsaka Rin has had a huge improvement, and she is pretty likable now. The most significant change I've seen in terms of character, is Shiro's. The hopelessly pathetic sorry piece of shit in Fate/Stay Night (2006) has turned out to be full badass in UBW; I hated him in the 2006 one, and was quite disappointed that he wasn't killed off by the end. However, his UBW character is the definition of a shounen anime/manga protagonist; it's as if his UBW character was finally provided with some balls, which the original clearly lacked.
It's one of the few anime I've really enjoyed in 2014-15.
Give it a watch if you're in for a ride.
(P.S. Some of the subs don't make even the slightest of senses, so bear with it, or wait for it to be updated with better translations)