The ending - probable SPOILERS

Well, I was disappointed when I saw the ending. Very disappointed! However, I've read things here and I watched the key part of the ending again and here's what I believe (and screw it if it's not what the director wants me to believe )...

After Caine was shot and got into the elevator, he finally got angry about the whole thing. He went back to the 5th floor and either killed the guy, or went through a delusional sequence and thought he killed him. That (overly long) so-called "blood" sequence could represent either of those two events.

Afterwards, the cops in on the conspiracy covered everything up and let him go because they figure that Caine thinks it's all over: his wife's killer is dead and he'll never find out any more about why she was killed. If he didn't think it was all over, I don't see him just driving away at the end of the movie.

That's pretty much it.

There are some events earlier in the film that might tend to lead one away from this explanation, but I choose to ignore them. Because any other explanation would make the movie suck (for me).

"The more you drive, the less intelligent you are"
-- Repo Man