When I saw the low rating this movie received from other people, I was expecting a typical poorly written, poorly performed, poorly shot movie. This was anything but. The entire cast (okay, so that's only five people, including two who never appear on screen) gave an outstanding performance. Lauren Martin (Celee) in particular demonstrated excellent depth of character and frankly, if this had been a major studio production, might have won an award for it.
The writing was powerful and overall well paced, with a good mixture of tension and twists. This might not have been a big-budget film, but it doesn't show in the cinematography, which left little to be desired. The basement scenes were a little dim to be fully appreciated but, well, it was a basement.
The only thing I can really come up with for the negative side was the length. I think tightening things up by about 8-10 minutes would have made it a faster, even more compelling movie without significantly hurting the character development.
Personally, I loved the ending (and definitely didn't see it coming), though I can see how some people might find it unsatisfying.
Overall an excellent movie, better than many major studio mass market films.