Austria, 1813. Two soldiers are on their way home to a small village in the mountains where one of them has a cabin that belongs to his family. They arrive and settle in, both suffering trauma from the horrible war. During a trek in the woods they come upon the mangled remains of a gypsy bearing wounds that clearly aren't made by any animal they know and during the night they are attacked by some kind of creatures, intelligent beings that leave a message. They want something from the men. Females to mate with.
Then we come to the maybe not so good things. The script for instance. The story is sound, pretty damn dark and interesting but could easily have been trimmed down at least twenty minutes (it's 106 now) to make it a leaner experience and the first half has a pretty damn slow pace. The acting is also not particulary thrilling, the leads are both fine but some of the lesser characters are not so much acting as more stumbling through their lines. Not enough to take you out of the enjoyment of the movie, just enough the lower the grade ever so slightly.
The horror bits on the other hand are mostly done well, even though the filmmakers chose to show very little of it for what I assume to be budgetary reasons, which is a damn shame. There is a great scene half way through the movie when one of the main characters find the cave where the creatures have been taking their prey and has to hide in a giant pile of mutilated bodies, only to find that one of the victims is still alive and will most likely make the creatures aware of him being there. The choice he makes here is pretty much telling of the morals of the characters here, they make a couple of not so good decisions that I won't go into for spoiler reasons.
So, in short, Tartarus is a decent enough little scifi/horror (yes, the creatures come from space. You get to see that during the credits) that could have used a lot more work with editing and little more on-screen grue. It's flawed but I liked it though I would understand why it might be a test on other peoples patience, people who aren't prepared to give kind of flick the patience it deserves.