This comment might seem harsh, I know he's getting popular and I do like him overall, but he's got miles to go yet. As nice as his attacking play is at times, he still has 2 assists in 50 games for the club and he's 27 in May.
He is seriously lacking in end product, it seems like he can do everything right until the final ball, which is almost always a total let down.
He is never going to replace Walker on the basis of good midfield play alone. Walker is the best defender in the world in open space, and his ability to mark pretty much 1/3rd of the pitch on his own and shut down breakaways and counters is absolutely crucial to the way we defend, and the backbone of how we play against anyone who sits back against us.
So to replace Walker his attacking contribution needs to be Dani Alves-esque, and it's nowhere near yet. He needs to start churning out assists and goals and being one of our biggest attacking weapons if he's going to be first choice RB.
Also for anyone praising his defending, I'd suggest rewatching the Arsenal goal yesterday...he's bypassed like a cone on the initial attack and then doesn't get within 5 yards of Martinelli which is why he has all the time in the world to put a good cross in. Then the ball comes out and he's caught sleeping so Martinelli has a free run to the by line to put the cross in with no defender near him.
Seriously, watch him during this and tell me he's a good defender -