Yeah, he's obviously got some ability but just doesn't seem able to use it to actually hurt teams or make himself useful. Apparently he did better at Preston, albeit still didn't set the world alight.
He's also one of those players who doesn't seem to have an obvious position. Is he a striker? A winger? Possibly best suited to the right of a front three but even playing there you need to carry more of a goal threat and/or be more involved in games than he seems to be.
People slate Woody for picking Gestede against Swansea (and rightly so) but Nmecha was an even more mind boggling decision.