Nice work, but there are a few things killing the likeness for me.
His eyebrows seem far too high and arched, and his cheeks too gaunt. He also looks a bit malnourished.. despite being a monstrous purple titan, the guy usually looks very healthy with very full features. I would push in the crevices in his chin more, perhaps inflating the areas in between some.
Here's some ref:
I also think the anatomy could use tweaking on the upper torso, and I think it would look a little cleaner if the bust were cut off in straight lines rather than more organically follow the anatomy.
Also, I agree with ScoobyDoofus, his skin is too light.