Grendel is based on the epic poem Beowulf, composed sometime between the 7th and 10th centuries by nobody knows who, which has seen a surge of popularity in the last few years. I know of at least two recent theatrical movie treatments, one written by none other than the uber-cool Neil Gaiman. Last night we got to see the Sci Fi Channel's version.
The basic story involves Beowulf (Chris Bruno), the Badass Warrior Dude of his time, and his quest to rid the kingdom of King Hrothgar from Grendel, a monster who sneaks into Hrothgar's mead-halls when the warriors are all drunk and pulls their arms and legs off and eats them. Apparently he doesn't like to hear people having fun. So Beowulf, being a Badass Warrior Dude, goes to help out.
Ben Cross (Chariots of Fire, Dark Shadows), an old favorite of mine, appears as the aging King Hrothgar, and he looks damn good. In fact, he gives the best performance in the show, and looks hot doing it, and is the only reason I managed to watch this all the way through. He's a good actor, and seems to me to deserve a higher profile career than what he's had. Marina Sirtis (Star Trek: The Next Generation), however, as the insane Queen Wealhtheow, looks pretty ragged, but that could be more because of her character's craziness than anything else. For some reason they decided white-face makeup would be good to convey insanity. An odd choice, that. Grendel and his mother are mediocre CGI creations, and the fight scenes look like they came out of a video game. The script itself is stilted and uneven, and the performances in general either over the top (Sirtis), or wooden and dull (Bruno).
So while we wait for the Neil Gaiman version, currently in post-production, check out the original (available at about any bookstore, or as a free etext at gutenberg.org), or some rather better adaptations such as Eaters of the Dead by Michael Crichton (adapted into The 13th Warrior, starring Antonio Banderas), or Grendel by John Gardner.