This episode probably ranks amongst my least favourites of all time. Despite having a few good gags, it's pretty boring and silly most of the way through. First, let's deal with the good aspects of the episode. It has an interesting concept: a Christian planet kept in the Dark ages by Sokar pretending to be the devil. It also gives us an interesting look at life back in those times, and their ridiculous methods of witch hunting and 'cleansing' a person of evil spirits.
There are also some pretty good gags throughout this episode. The recurring gag with Jack telling Carter "If I ever get the urge..." and "If Daniel ever gets the urge..." is pretty good, but we've seen much better from the show. But there are some great, arguably classic gags such as Jack's Dr. Evil reference, their discussion on the Bible, and of course Jack being ever so grateful for ol' Junior.
But the episode has some serious flaws. For instance, the Unas doesn't really come across as menacing, and is at times pretty pathetic. The makeup looks really fake at times, especially its picture on the outside of the DVD box set (I really don't like looking at it). Having it voiced by Christopher Judge only makes it less real. Unfortunately due to the amount of make-up, production and costume design in this episode you can't really forgive it by calling it a budget-saver.
But the episode on a whole is pretty boring. Stargate usually strives at being a very entertaining show, but there is always the rare exception and this is one such example. I also really don't like the thing with the Canon and his lightning-ring. Firstly, it doesn't make any sense as we've never seen the Goa'uld with this kind of technology (with the exception of Anubis), and secondly it looks really silly when it stuns SG-1.
On the whole, this is a rather disappointing episode. Sure it has its funny moments, but it could've been so much better.