He's clearly a good player because he's scored a ton of goals last season and had good records at other clubs.
This season has been very stop-start for him. First couple of months he was in and out as Haji, BTA, Bassette all competing. I think he had a couple of good games, particularly against Luton at home, then I think he was injured and didn't play again under Robins. Under Lampard, he's scored goals in 3-5-2 but not so much in a 4-3-3.
As for what he's good at, I do think he wins headers and brings others into play. His touch isn't great, he's not aggressive enough and he's a confidence player, which all do hold him back. Maybe his strengths are more his natural assets rather than skill but that's fine.
At this level, he's a good striker if you can either play to his strengths or have a team that compliments him. He's not a world beater. He's definitely got limitations but at our level, that's standard. The point is, he's shown he can score goals in the Championship.