I simply can't get over how brilliant the pairing of Walter Matthau and Jack Lemmon is. It's like the movie doesn't even need additional characters because you can never get tired of the dialog between these two.
Lemmon had already been in several well-known films like Mr. Roberts and The Apartment and Matthau was fresh off his Oscar win for The Fortune Cookie (another Billy Wilder film also with Lemmon). That particular movie wasn't as great as this one because the story couldn't sustain such a long running time (I think it was almost 2 hours). However, this goes by at a brisk hour and a half, even though the introduction of the events leading up to Lemmon ending up at Matthau's apartment is a tad long (so was this sentence). That's a minor quibble though and for the rest of the running time you have a marvelous time.
I have already written a comment about how the follow-up to this film sucked and I won't go deeper into that. The reason why this is such a joy is probably that the movie was made just as the innocence of American movies was beginning to fade fast into oblivion. There are some sexual references but they are dealt with in such an innocent way that you couldn't even get a "Well, I never..." out of the most prudish person out there. It is kind of fun to see a movie from a long lost era and that was probably why the sequel didn't work because you had Matthau and Lemmon say quite a few f-words and that just doesn't fit them.
Of course, now they are both gone and you can just be happy that you still can enjoy them in a marvelous film like this. I think the only male actor in this film who is still alive is John Fiedler. Edelman died recently. So there you have it. Simply one of the best comedies and films ever.
Add: I have just learned recently that John Fiedler has died so to all the fans of him I am deeply sorry. I didn't mean any disrespect and I will try to be more careful of what I am blah blah blahing next time.

A young man kills a young woman for no reason. The man's brother is jailed on charges that he was an accomplice, but soon escapes. Upon escaping, the seemingly innocent man kidnaps three victims and soon he ropes his girlfriend in on the plot. If this isn't bad enough, the situation quickly makes a downward spiral.
This film had some good aspects and many bad ones. Its strongest aspect was lead actress Emily Haack. Setting aside the fact she's nude in a fair amount of this film, she presents herself as a decent actress and a very strong character. I see no reason she cannot take this experience and somehow turn it into a career in some way. I was convinced she was a ruthless individual.
Also, the makers of this film were very bold and pulled no punches. Graphic nudity (both male and female), coprophagia, and extreme anal violence are not shied away from. I like my horror films to push the boundaries a little bit, and this one ignored them altogether, gladly skipping towards Gomorrah. Maybe it was too much, but I think they achieved what they were looking for.
But now the negative aspects. First, and most noticeable, this film is very low budget and the film quality shows this. I can excuse that -- the plot was decent, the acting fine and in some scenes the lower quality film actually made the movie more disturbing (a more realistic feel). So, I won't scold them for having low-grade equipment. What I will scold them for is the use of poor choices in shots. For no reason I can ascertain (besides plumping the movie), there is a large amount of footage of a cemetery. I don't really know why, and I frankly started dozing off at this point because it was so long and pointless.
I also take issue with the title. The idea here was to deceive people into thinking this film had some connection to the classic "I Spit on Your Grave". Now, there is a line that seems to imply the main character is the daughter of the woman from this other film. And the themes are very loosely the same (a woman getting revenge on men). But there is no firm connection and the reason this title was chosen was for the video store customer to think they were getting a sequel. This was deceptive and dishonest.
My last major complaint is that this plot makes no real sense. Not even a little bit. A woman is killed in the beginning for no reason. A prison escapee finds time to kidnap people to torture them, for no reason (because they wronged his girlfriend?). The same man goes from good to very evil without explanation. Likewise, the female lead (Haack) turns fro ma normal person to someone who is overly cruel and sadistic, for no reason at all, and against people who for the most part were only marginally mean to her (a neighbor offering drugs for sex is wrong, but by no means worth getting tortured for).
Don't let this title fool you, or the claims that the film is incredibly shocking. Yes, some scenes were shocking, but the vast majority of the film is dull and makes you want to take a nap. If you see this in the video store or on Netflix, just keep browsing. Or rent it, and we can sit around and vent about it for hours. You have been warned.