The new TF2 update is sweet. I'm going to briefly review all the new items. (Later I'm going to post about all the trading I've been doing. Basically, I've been robbing people, and they say "thanks" at the end.)
Vita-saw: Worst item in the game.
Gloves Of Running Urgently: Heavy has been waiting for this for a long time, and it is worth it*. This makes the Heavy infinitely more valuable for 5-point capture maps, since the Heavy can arrive at the center point with the rest of the team, and can run to capture the next point with the team, instead of showing up late to everything. I would pick these in 100% of situations.
The melee damage reduction is trivial. If you're doing melee with the Heavy, you're doing it wrong.
The damage over time can actually be beneficial if you're with a medic; the self-damage serves the same purpose as a soldier shooting himself, making the über charge faster.
The Scout Pack:
This one seems crazy overpowered. If you have the hat with these items, you get +25 HP. If you don't have the hat, you don't. How is this not getting bonuses from a hat?
The Holy Mackerel: The best item in the game.
Shortstop: Seems good, but I haven't had a chance to use it. The slow effect is hardly noticeable, mainly because you die before you have time to check what's going on.
Mad Milk: I definitely like the idea, but again, I haven't had a chance to try this one out. Seems like it would work very well if both teams were meeting in large groups and you milked a bunch of their team at once. It would basically become a heal effect for your whole team for the duration of the fight.
The Soldier Pack
The item bonus for the Soldier pack isn't as good as the scout pack, but it's still a pure bonus. Sentries are often rather binary: if you get in the range of a level three sentry, I don't think a 20% resistance is going to save you.
The Black Box
The Black Box works as a spam weapon for long distances. I don't see a place for it in competitive play, but I could imagine someone playing long range spammer in a public game. It's especially good in pubs because there are so few medics. There's basically no way to use this gun for dive bombing people or other close up fights though.
Battalion's Backup: I'm not sure about this one. The true power of it is canceling critical hits, but I don't know a way to anticipate crits in a timely way. I'd be very impressed if someone managed to time this against the activation of a Kritzkrieg.
The Pyro Pack:
This set bonus is far more balanced. You get 10% more speed, (making you a little faster than a medic, but a scout is still much faster than you), but you gain a 10% vulnerability to bullets. I'd really like to give this one a try, even though I don't like the Powerjack.
The Powerjack: The natural comparison is with the Axetinguisher, and the Powerjack comes up short. The damage bonus for the Powerjack is trivial compared to the Axetinguisher's 195 damage crit. The bonus 75 health for getting a kill with the Powerjack is cool, but you have to be psychic to know when the enemy has enough HP to die from a single hit, and you really don't want to have to swing with it twice.
In other words: to get the bonus HP you need kills, and it's too hard to get kills with the Powerjack's damage output.
Degreaser: I love the Degreaser. The weapon switch is unbelievably fast. It's possible to set someone on fire, switch to the Axetinguisher, and get your free crit in about a second. It also makes it much more practical to switch the the Flare Gun or Shotgun for long-distance spamming, then switch back to the Degreaser for reflecting rockets and other projectiles. The reduction in afterburn damage is almost trivial; you lose 17 damage over the course of the fire.
I'm pretty sure this uses the sound effect of the flamethrower from Alien Swarm.
The Sniper Pack:
This is another "purely better" equipment pack. If you have the hat, you cannot die from headshots, and if you don't have the hat, headshots can kill you. There is no trade-off whatsoever. Top Tip: If you do have this hat, Don't move around when you're fighting another Sniper. You want them to headshot you, instead of killing you with a bodyshot.
Darwin's Danger Shield: I know I wouldn't use this item, I like Jarate too much. But maybe someone would run this with the Huntsman as a close range sniper.
Sydney Sleeper: This is the sniper rifle for the real team player. You're not going to be getting nearly as many pro kills with this thing, but you may get a lot of pro assists. A good team will focus their attack on the person you've "marked", which allows you to designate targets. If you want to use the Sleeper but still not use any teamwork, you could try it with the SMG. People would be much less willing to attack when you have a mini-critting hitscan to repel them.
Bushwacka: This crits instead of mini-critting. How are you going to get minicrits? You're probably not going to be going into melee with the Buff Banner, so that leaves Jarate and the Sleeper. This is basically a defensive weapon. If someone gets close, you throw Jarate or hope you shot them with the Sleeper, then you go for melee. I like it.
The Spy Pack:
This is one of those item sets that's like playing a completely different class. With the reduction in watch sound, this pack is clearly for the Dead Ringer. With the Eternal Reward, this means that you can't disguise and you can't turn invisible except in very narrow situations.
The item description "0.5 sec longer Cloak blink time" is rather obscure. I guess I shouldn't be surprised that Valve has been bad at expressing themselves again.
Your Eternal Reward: This is a really neat item. As with all spy items, people will get used to it and return to hosing Spies soon enough, but right now, it's still taking people off guard. By instantly disguising as the person you've backstabbed, you're invulnerable to sentries. Since the backstabs are silent, it's much easier to chainstab people.
L'etranger: Getting a little more charge isn't that important, unless you have the Dead Ringer, which requires a full charge to activate. Unless you're using the DR, stick with the revolver.
They're good for trading to people with more money than sense. There's less than a 5% chance of getting a special hat. Logically, this means the unusual hats are worth more than 50$ of keys, plus the cost of getting the crates. Also, there's a good chance it won't be a very good hat. If there's a 50% chance of getting a hat you want, then those hats are worth 100$ of keys. To be clear, I'd love to have a hat with a particle effect, but there is no way in hell I'd spend real money to gamble for one, especially with a 50% chance of getting a normal weapon or normal hat.
*When they increased the speed of the Heavy's spin-up, spin-down, and walk speed when spun-up, I thought that was a replacement for the GRU. Now the he has both, Heavy will be a true beast.