He's still coming back to full fitness, so it's not fair to dump on him at this point.
I think he's great, personally. Totally shuts down his flank and forces his opposing winger backwards. It's true his attacking threat isn't great, but he rarely loses the ball, always makes himself available for a pass and wins more corners/throw-ins than anybody else in the squad. In terms of retaining possession, he's an exceptional option to have.
The way he dominates his side of the pitch, he almost makes the game 10 vs 10. He cancels out both himself and the other side's winger. Given that most teams have their most creative players on the wing, what Valencia offers is invaluable. Pooh-pooh that if you like, but there's a reason that all his managers have loved him. Some aspects of football are about what you discourage the other team from even trying.