Yesterday night, they introduced a pretty big TF2 update. Since it improved my favorite watch, the Dead Ringer, it inspired me to do a list of the best updates that TF2 has done, in order. It will naturally start with the class updates, the updates following will be more interesting. I think that engie update will be number 6. Probably scout will be the last of the class updates, since it's lame.
#1: The Sniper/Spy update.
Of course the first update is the biggest one. It has a new gametype, two classes being updated with awesome items, (except the Cloak and Dagger and the Razorback) and the new item system. You may not like the system, but there are hats too, so I think that's a trade off I'm willing to make.