TA may not be a great playmaker now and may never be at the NBA level. But he's got the prototypical size, length, and athleticism/quickness for a wing player. If he can rebound, play pesky D, and finish... And hit 35%+ on 3's... Well that's a serious rotation player, especially on a team with a dominant all-around wing like Carmelo.
You can see some things he can do well based on the highlight clips.