No proper escape mechanism as well, Imprison requires your team to actually use the time to come help you or you just delay dying by 4 seconds. And of course BKB means he is useless which is a pretty big deal if you're trying to carry.
His primary source of damage is magical and requires constant casting to sustain. If he is silenced he literally hits for a third of the damage he normally does. He's squishy and has no real escape mechanism. His ult is pretty good, I guess.