Krull isn't exactly what I would call a great film, but it's a fun film with imagination to spare, and any time there is sci-fi or fantasy that is even half-way decent, I feel the need to support it. Krull exists in the sort of Flash Gordon world of something that isn't quite camp, isn't quite nostalgia and isn't quite retro, but certainly isn't modern. It's a film that doesn't sit squarely in any camp, and that made it something of an odd man out, but no less worthy of your attention.
It's hard to say which half is stronger - the fantasy or the sci-fi. The core conceit is very fantasy: a princess and a prince are scheduled to be married to form an alliance between two rival kingdoms, so that those two can unite against a greater foe. The wedding is attacked (by said greater foe, naturally - the ominously named Beast and his army of Slayers) before it is completed, the princess is kidnapped and the prince is the only survivor. As the hero recovers, he learns he must seek out a mystical weapon known as "the Glaive" and travel to the Black Fortress, a mysterious building that moves every day at sunrise.
I can't tell you that Krull is a great film, because I'd be stretching the truth there, but it is a fun film, filled with imagination that is bursting out of the seams at every opportunity, and it also includes a very young Liam Neeson as one of the bandits who helps the prince along his quest. Critics didn't care for the film at all during it's time, calling it nonsensical and boring. While I can understand (and even agree with) the nonsensical, I certainly wouldn't call Krull boring. It strikes me as the kind of "well, why not" approach to storytelling that can make for some fun stories. The prince is a fun character and is going through the typical hero's journey, but the lack of distinction between the sci-fi elements and the fantasy elements tends to put people looking for their films to "make sense" off-guard. (Many of these people also don't really understand the appeal of "The Adventures of Buckaroo Banzai Across The 8th Dimension," so what do we care what they think?) To me, this is the kind of over-the-top film that used to be standard Saturday afternoon fare, with larger-than-life heroes and villains. I think if they had stripped away either the sci-fi element, or the fantasy element, or both, this would've been better received, but it certainly would've also been a lot less memorable. If you can't turn off your need to question why things are the way they are, then Krull isn't for you, but for those of you who aren't afraid to dream big and don't mind things being a little silly along the way (and, y'know, watching films with 1980s-era special effects, which rarely age well), I think you'll find Krull has a big heart and great sense of wonder to it.