I like the saw movies for the all out gore, but also for the surprise endings. III was better than I and II for gore, but the surprise ending, wasn't as sudden. A lot of people who go for the ending say they didn't like it because the ending was slightly more drawn out:
<spoilers>
The viewer knows JigSaw's apprentice (Amanda) is faltering when the female detective can't get out of her ribcage trap, and also when jig says that Amanda's life depends on the doctor, you can kinda tell that jigsaw is messing with Amanda too. The thing that I still enjoyed about the ending was how, by playing his last tape recording, jigsaw knew that the guy would lose his entire family (son, wife, and now his daughter is trapped). He says that there is one last game to play (when you see the girl through the keyhole). Another cool thing (for potential sequel / Saw IV) is how jigsaw says how the guy failed his test of forgiveness, and he can continue his wrath; jigsaw offers him all of his supplies and tools.
Anyway, the gore was spectacular, and the ending--for me--was still fulfilling. Nothing like the first one (OH SNAP THAT GUY ON THE FLOOR IS ALIVE!)
</spoilers>