The new map, Pipeline, is really cool. And the achievements are really good too. I got many of the ones that you get for being super-cool.
There's an achievement for killing someone with the Spy's knife-taunt. You can kill someone with the knife taunt while you are invisible. This also destroys buildings. I was running engie, and I got killed along with a dispenser and a sentry without ever being able to see my enemy.
The alternate weapons are cool, or so I've been told. See, Steam doesn't want me to use the new items, so they've devised a system of giving other people random items at random intervals, and never giving me any items under any circumstances. I've played for over 4 hours since the update, and I haven't even received an item I don't need!
Let me clarify: As far as anyone can tell, the only way to get the new items is to simply play TF2, and the system rolls dice to see whether you get anything. Not only do they give you extremely few items, demonstrated by my complete lack, but they also give you a random item including the items you already have. Let's say that I get an item at random every four hours. Since there are twice as many old items than new items, I only have a 1/3 chance of getting something I might want. So every 4 hours, I have a small chance of getting an item I may want.
I'm OK with separating Achievements and Equipment, although I think there's an argument to be made for it, but completely separating the player from his ability to gain new equipment is a mistake, I think.