I will second Spore for the reasons mentioned above and its another triple A title focusing on user generated content, but also it had the most intense DRM requirements of any PC game, ever. That shows something about the industry in regards to what its attempting to do against piracy.
I will also second Braid in that it shows how a indie game can become relatively mainstream and profitable in today's market.
Now for the third I'm rather unsure of one specific game to pick. This was probably the year that really shows the future of the Triple A titles in that companies are desperate to find a solid franchise in the recession. So I think a game like GTA 4 shows a solid game that is built upon an old franchise and will probably continue to exist for many years.