I'd like to do some sort of "/r/Games's Favorite Games of 2012", but how could we do it that's interesting and not prone to abuse?

r/Games was created shortly before the end of 2011, so doing a "Games of the Year"-type vote last year wouldn't have made much sense, but since it's been running for all of 2012 I think this might be something interesting to try out. However, trying to do poll-type things on reddit generally works quite poorly for a few reasons, so I wanted to see if anyone had any thoughts about how we could take a decent shot at this.

We definitely don't want to do it in the "vote up the comment with the name of the game you want to vote for" manner, because that has all sorts of flaws and biases with it. So what I've been thinking is to set up a bot that can receive private messages containing your vote(s). When the voting period ends, I'll get rid of any invalid votes and then tally up the results and post them.

There are a few decisions to make though, and this is where I'd like community input:

1. What, exactly, should we vote on? A single "best game of the year"? Or should we allow each person to submit something like their top 3 or 5?
2. Or alternatively, should we make things a little more complex and split voting into a few categories? If so, what categories would you like to see?
3. How should we determine whether someone's vote is valid or not? Back when I used to moderate r/gaming I had a similar voting bot for "What's r/gaming playing?", but after a while it just became something that various game-specific subreddits spammed to make their game look more popular than it actually was. I want to avoid a similar thing happening here, so there should probably be some way to remove the votes of people just trying to influence the results. Would it be reasonable to do something like check whether they had any submissions or comments in r/Games previous to Dec 1 and disregard their vote if they didn't? Any other method that might work?

(If the voting system ends up involving categories and such, I'll probably set up a website somewhere where you can make your choices, and then it'll give you the text to copy-paste into your PM to the bot, just to make sure votes are formatted properly.)

Any other suggestions or thoughts about how we could do this?