Lennon before his injury last season was the best winger in the league I thought, he was a changed player - he was crossing from deep, he was picking out players, he was cutting in(off either wing) and taking a shot, and in general he improved in the areas he was mainly criticised for, IMO.
A brief example of him now taking more time to pick out his man, and showing a willingness to cross from deep rather than simply get to the byline and fire it in, would be his cross for Bale's goal at the weekend.
I'm not saying he is or isn't better than Valencia, we use him in a fairly specialised role that most wingers can't play - he's vital in pressing the play high up the pitch and allowing our midfielders to advance and compress the opposition midfield, and he provides plenty of cover for a position that we've had a few problems over the past year at right back, for a couple of examples.
Lennon's definitely showing signs of improvement though, when it looked to me like he might have stagnated somewhat. Last year he had more assists than he'd ever had before despite only playing half a season.