Most ADCs don't really have much in the ways of impressive abilities, and Twitch'es Ultimate, passive, and stealth capabilities are certainly noteworthy. He's not bad at jungling either, which is nice when bruisers are strong enough to destroy typical ADC+Support lanes. His ganks are actually pretty terrifying, coming from being on the receiving end there. His passive is fairly potent, and his attack range and Expunge can cause you to loose 50% of your health when you've already retreated to your tower. Being able to turn invisible and bypass wards is always a plus too.
I'd say Twitch is good now. I'm not sure why I don't see him more often.