I'd say it's definitely worth watching. It's not a top tier movie but if you're looking for an action packed movie with great production values, you can't go wrong with it. More than anything else UBW excels at looking amazing with its battles and if you're looking for that then you'll enjoy it.
Judging from your sig, you're already into the Fate series so you don't have to worry about that prerequisite. One thing I've always told people is that Unlimited Blade Works is by far the worst installment of the Fate anime to begin with, just because it's so fast paced that someone who hadn't watched the anime or played the visual novel before would have no understanding of it and could not possibly follow the story. But if you've already done one of those, then watching UBW is just fine and you should be able to follow well enough. I for one have yet to play the UBW route of the visual novel but I still thoroughly enjoyed watching the movie and could understand it for the most part, though it's true that it was rushed and not everything was thoroughly explained.
One thing I've come to realize is that the visual novel is probably the best way to go just because it gives all the details and important story elements that both the TV anime and the movie skip over, but the catch is that the visual novel takes an insane amount of time to complete. I've only played the Fate route, but even then I can say that I would probably have been able to finish the TV anime once or twice in the time it took me to get through the VN route because it's just that long.
But yeah, if you've already seen Fate/stay night, definitely watch it. I'd say it's better than the TV series, but don't look for a masterpiece level plot because it goes so fast that it can't really focus on it. But in terms of presentation and action, UBW is fantastic.