If you watched Fate/Stay Night which is the first series made of the Fate games you will most likely want to have a look at this movie. Unlimited Blade Works is based of the second route of the Playstation 2 visual novel called Fate/Stay Night Realta Nua.
The first thing i could noticed in the movie was that the pacing was really slow as in the first part of the movie, when the movie comes about halfway it gets a little interesting if you have seen the first series cause some little revelations about Archer.
Unlimited Blade Works simply gives you a new show. It takes time to get to a particular point in the story where it was still similar to the tv-series, but from that moment on the show takes a whole different swing and leaves you wondering how they were able to create a story with these many different uptakes even without being completely unrealistic. Because that is what it is; the show never feels forced and it never feels like they created a different ending to the series and despite you knowing how the other path went, you still feel like this one is just as natural.
The criticism I can offer is that the movie feels rushed. In the series internal character struggles needed time to think things over, whereas the movie skipped most of them in order to focus on the plot. That is pretty much the only thing I can think of where the show should have slowed down some more in order to get the characters more into the story, rather than the story dragging the characters to where they should go.
It’s a good thing that we already knew most of the characters(if you watched the original series), otherwise they would be fairly flat in terms of development. there is not much happening to them. Sure there is some character development, but that’s pretty much only focused on the protagonist and another person.
As for the animation, if you where to compare it to the series it looks much better this time around. The backgrounds look like they have been ripped straight out of the game at times, but the CG backgrounds simply look terrific thanks to the detailed parts and the way they added light reflections to them. This time around they played a bit more with the lighting. And what I personally like most is the clothing; how the wrinkles you see in them due to the clothing being worn by its owner.
As a conclusion i would say that you should watch this if you have some sparetime over as i did not find much value in it. I would also recommend you to watch the original series before you watch this movie, otherwise you will most likely have a questionmark on your head.