Yeah, but late game bulkiness makes sure twitch can't really kill you. He's AA focused and has the ability to jump you, but has very few strong steroids to buff his damage (Q buffs his dps, W helps get stacks faster, E is nothing more than a "nuke", and R only gives a slight AD buff). The only way he has of getting through health, the main bulk stat, is
, which only works if he can auto you down for a good 5 seconds, then E you for the remaining, what, 300 health? If he's actually trying to be an assassin and get picks, it won't end well for him unless he goes for a squishy. Target the enemy ADC? All the popular ADC's right now are pretty good at bursting practically anything, so if you pop up too close they'll counter damage you, pop up too far and they'll just walk away since he has no way to really stick (ironic considering all the sticky stuff he probably has). Target the mid laner? If it's an assassin, lol gl. A mage? It might work if you really get them by surprise, since they have no way to survive outside damage.
Way I see it he should be a slippery, stealthy dps god, and he was for awhile, but with all the changes to the game in the past year, along with all nerfs he's gotten, hes fallen flat. He just needs a few changes here and there to make him really stand out.