You'll want to consult the notes
When Valve first talked about the most recent Team Fortress 2 update, the focus was placed on two new community maps, "Process" and "Standin." Looking over the extensive patch notes now, however -- they keep going and going -- there's a lot going on here.
Old maps have been revisited, items have been tweaked, and yes, there are now Summer Coolers and Keys to worry about. I'm no expert on the metagame by any means, but many of these changes (50% overheal for the Quick-Fix, I'm looking at you!) sound terrific on paper. This is all going to make for an exciting, crazy time.
Darn it, Team Fortress 2 -- I've started playing you again. And there's no sign that I'll want to stop anytime soon. So long as I don't simultaneously get into Dota 2, I'll be okay. Wait, I'm screwed.