Talon is an assassin. He is one of my favorite champions, and one of my best I think. He snowballs really hard, and it is fairly easy to carry games on him.
He is usually sent mid since he naturally counters APs with his E (it blinks him to them, and silences them) and the amount of damage he does. It's not uncommon to take some from 100 to 0 in one rotation of your spells, though I usually take ignite too, so you get that little extra oomph. He doesn't really do anything if he doesn't get items, which is probably his biggest downfall. And since he has a melee auto attack he can be denied if the other person is playing correctly. It is hard to zone a talon though.
He can be played solo top, but I prefer him middle. He doesn't trade well with bruisers and usually ends up losing top. Not always, but a lot of the time. If you are playing ranked or draft, top is more viable since you know what you are going to be fighting, but taking him top in blind pick is really risky.
I also play him bot with karma or leona for a kill lane. I'm not going to say that's how talon should be played, since it's pretty much a gimmick, but it usually works and it's really fun.
I haven't played him much in ranked, so I don't really know if people know to counterpick him, but I think he is best used as a counterpick. If you're just a really good talon player you can pretty much kill all the mids, but you will lose to someone eventually.
I would pick him up, he's a really good champion to have. He can be jungled, but I honestly think ezrael is better at jungling than talon.