I like Fate Stay/Night, so my opinion is biased. The movie starts out with the first UBW chant. (I like it already :) Plenty of exposition is skipped, (see aside) and the action starts around 4 minutes into the film, as the concept is being explained.

Aside: To any unfamiliar with F S/N, it's a visual novel with 3 paths/stories in it. There's Fate, UBW, and Heaven's Feel. The Fate story branch was released as a 24 episode anime. That should give you a good idea of how much material they had to fit into a roughly 1 hour and 42 minutes movie. (not including credits) To those familiar with the novel, you may notice some inconsistencies, which I guess were put in to make it shorter.

Characters- I like a lot of the characters. Shinji is a jerk, as always. Rider doesn't get much time in the spotlight in UBW, unfortunately. Berserker destroys everything, as usual. Ilya doesn't get much time in the movie. Lancer is cool in UBW. Caster's kind of a jerk, as is her nature.

Shiro - A nice guy, too much so. But he manages to not be entirely lame because of it, which is quite a feat. Archer - Sort of a jerk to Shiro, but cool in general. Plus his abilities are just too awesome. I can't really say more without giving away spoilers. Saber - because UBW is about Shiro, Rin, and Archer, she doesn't get much time/exposition. Unfortunate, as she's one of my favorite characters. Rin - the shortened movie doesn't give Rin as much depth as she has in the novel, or highlight how antagonistic she is at first.

Scenes- When one finds out which Hero Archer is. Archer's last major battle against (too much of a spoiler to say but you should know if you're familiar with FSN) The final battle. Any time Unlimited Blade Works is used. The fight against Berserker at the start. When Lancer throws Gae Bolg.

TL;DR/sort of summary

It's a movie based on a visual novel, heavily edited to be short. Magical familiars called Servants (who are heroes of legend, like... Achilles, or Lancelot) are summoned to fight for the Holy Grail, which grants a wish to the victor.

I can only review this as to how it compares to the novel. There are several plot details cut out, and exposition. But there's nothing that can't be understood because of it. However, to know everything that's happening, it would appear that one would have to either have a basic knowledge of what happens or would have to watch it a few times.

9-10/10. I am biased though. Plus, I am thinking of it as much in terms of movie to novel as I am thinking of it in terms of entertainment. They did a pretty good job of fitting a lot of material in a little space.

IMDb says 7.2/10 right now. Well, first, there aren't many ratings on it yet. But I could definitely see giving it a 7-8 if I saw it without being familiar with it. I'd be a bit frustrated by not knowing everything, maybe.

The war for the Holy Grail is on. Master/Servant team pairs made up of Magi and the summoned spirits of legendary warriors do battle to the death in their quest for the right to claim the prize. The winning team claims the Grail and it's power to grant each of them a wish.

The movie even though majority of it was a recap of a few of the episodes I thought it was a pretty good take on the series even if it changed certain things. The animation even improved a bit from the show as well as a lot of the voice actors. Liam O Brein knocked it out of the park as Archer and his performance in this movie show why i prefer his take over the current guy.

overall good

I've followed Fate/Stay Night through the visual novel and Fate/Zero sequel, so I had no difficulty following this, -- it kept me in fangasm! The animation, color and shadow was as bold and beautiful as the VN artwork, and far superior to the previous anime, and the powerful music expertly finished the work. These are all the features that kept me involved in the only Visual Novel I've ever completely read, and this was just as satisfying.

The romance between Shirou and Rin was unfortunately overshadowed by the clash between Shirou and Archer -- but it's Archer, so I can't complain (got GAR?) Punches were pulled with Ilya, toning down her scene which still managed to remain appropriately disturbing (enough to leave even Ilya-haters in shock.)

However I was occasionally distracted by how confused someone would be if not familiar with Fate/Stay Night, or who had only watched the anime. It's still engaging to watch, but so much of the meaning was sped past or glossed over that it would leave most bewildered through it. It was also littered with continuity nods that would please the fans but be lost on the unversed viewer.

So the rating I give this is only representative of my own enjoyment of it, but isn't likely to apply to anyone who isn't a Type-Moon fan.