He doesn't have particularly impressive pace, quickness, or dribbling ability in one-on-one situations but he has quick feet and his football IQ, movement, composure on the ball, and vision are fantastic, especially for a young player. Basically, he is the exact opposite of Oxlade-Chamberlain. He works really well in the current setup because he offers a counterpoint to Walcott - a wideplaymaker to offset a traditional winger - and because he has the movement, touch, and speed of thought to combine with players like Ozil, Cazorla, Walcott, and Sanchez in very quick sequences.
His goals+assists statistics aren't amazing (although not bad) but they really understate his contribution to our attack. He has been in the middle of a ton of flowing moves, often delivering the ball to the guy who then delivers the final ball to a goal scorer. The second goal against Chelsea is a good example.