You don't really hold out much hope for a flopped prequel you picked up from a bargain bin. And it was one that has a troubled history at that. Two very different versions of the movie were made after the studio decided that there was not nearly enough action in the first. The first attempt was later released with the title Dominion: Prequel to the Excorcist and was directed by Paul Schrader. The second one was directed by Renny Harlin, who has made some fairly decent action pictures (Die Hard 2, Cliffhanger, Deep Blue Sea). Stellan Skarsgård features as the lead in both: a young Father Merrin, who saved/ will save the girl in the original Excorcist.
Merrin travels to East Africa to find a creepy artifact. Once there, he is told about a church that has been discovered, buried under the sand. Later on, he finds a crucifix hanging upside down over the altar. Not a good sign - surely - and indeed people duly start going insane, getting possessed or dying in nasty ways.
The movie has a couple of problems; the biggest one being that the script does not make much sense. When you take The Devil as your main villain you are setting yourself a difficult task; how do you define the powers of the Big Evil? What can he do and what can't he do? Why is he able to possess whole flocks of animals but - apparently - only one human at a time, though he can make groups of people act crazy? Why does he not just kill or possess Father Merrin when he has the chance? It is unclear what rules are being played by and why God, who by extension is part of the plot, would allow this. The ultimate goal of Evil is also a mystery. Tension is even more deflated when we realise that - since this is a prequel - Merrin is pretty much safe, though everyone else is probably toast.
Frankly, it's all borderline silly, which is unfortunate as the movie plays it very straight and Ominous. But enough nit-picking. The story is basically about Merrin finding back his Faith. And about a bit of gore while he does it. The movie's strong points are mostly in its looks: good lighting, beautiful sets, nice cinematography. In special effects its reach exceeds its budget a little bit, most notably during the over-the-top climactic scene, which falls literally flat. I'd check out the more artsy Paul Schrader version to compare, but life is simply too short.