EMG, ZED OP RITO NERF PLZ. Okay, sorry about that, but I hate the guy just as much as anyone else, but I somewhat agree that he's healthy for being an assassin which is where Talon needs to be. They're supposed to be quick, clean cut, get out, not "I'm gonna do major damage on so and so and hopefully survive as my blades give away where I'm at after I run." It'd probably be nicer for him if he could control where the blades went rather than always returning, maybe giving him a small refund on CD or mana/energy (haven't played against or with one in a long while, not sure what his power is) if he catches them sort of like Gnar with his boomerang. A lot of people I see when up against Zed make a problem of getting close to him which is bad and range is a better thing, since most champions are squishy, you'd be better off with some sort of tank against him like Sion or Braum. These are just my thoughts, take them with a grain of salt.
I've played a lot of Evelynn and she's pretty much Ult, kill, clean up with Q, although I might be playing her wrong. With her ult, she gets a nice shield that helps to guarantee a kill and her passive allows her to escape if she does the job or messes up. This is why you don't send assassins to kill the entire team, they are meant as 1v1 or possibly 1v2 in most situations, they're extremely squishy, just a little bit of CC and it's over.
Ahri could be an assassin similar to Zed, I believe that the developer wanted to make it so landing skillshots with her is essential to her playstyle. If you are good enough with her, a charm > foxfire > orb combo should be able to do massive amounts of damage, her ult should not be really used for pure offensive, it's to either escape, go in and get out, or be constantly changing positions so that the enemy isn't able to land their stuff on you, unless you're playing against a cheap champ where you point, click 100% hit such as Taric's Dazzle or Annie's Fireball.
Akali is, I would think, healthy as well. I've played with and against many of them and her job is kill, move, kill, move, hopefully taking out the squishies and getting out before the tanks arrive.
Fizz isn't an assassin, he's the devil incarnate who comes, kills and continues on as if he's on a Sunday stroll. With an ability that negates targeting, does AoE damage, tosses a fish that will 9/10 kill you, even if you're a tank. He's probably the only champion, aside from Vladimir, who aren't OP just because they're strong, but rather because they are extremely mobile, have low cooldowns, and pretty much cause a ton of damage in teamfights and 1v1s are like a game for them. Quite literally, he's a slippery fish which is why it's important to land your stuns, snares, and slows on him as fast as you can before he's able to pull off his bounce. While I think some champs might be too strong, he's one I'd personally say hit him as hard as you can with that nerf hammer, he can one shot you with a single R from full health.
Assassins: uber strong in 1v1, I take pleasure when I manage to snare them and hope my team smashes down on them.