Othello - What is with the creepy smile?!

Alright, what were Iago's motives at the end?! Why was he happy?! He is going to be tortured to near death and he is HAPPY?! It just makes no sense. So what exactly motivated Iago throughout the play? The whole time I was waiting to hear some big revelation of why Iago acted the way he did beyond the reasons he mentioned earlier in the story. Nevertheless, he was a cool character. All annoying-ness aside about how he ended things without coming clean about his motives, he was totally bad rear-ended for not spilling his secrets. I can't help but to admire a villain like this. Even though I am all for the good heroes, I love an even better bad guy. I don't really know what I am saying in this blog post; I mainly just wanted to get my questions out there that I asked about in the beginning. But seriously, what were his motives? Maybe one day someone will unearth a hidden sequel or epilogue that Shakespeare wrote...