Urgh. 2009. Now we're hitting the low point of my video game years. I pretty much played EU III, and then EU III some more, with the occasional foray into Pokémon (and one notable foray into Skyrim), for a while there.
Of the games I played that were released in 2009...PvZ was the one I had the most fun with, but it doesn't deserve a vote.
With that I'm going to go with counting Minecraft a 2009 release (first development version), and give it my vote. I may not have played it, but one has got to respect the impact it made.
If it's determined that Minecraft doesn't count, then I'm voting abstain.