I think the main issue with Federer is he doesn't really know which brand of tennis he wants to play now, and I can't fully blame him since it's not as easy as it sounds. Back in 2003, he was super aggressive. Then, with time, he really changed towards a more point construction oriented approach (of course while maintaining the aggression). A decline in movement means neither is that likely now. He just can't play an all out aggressive approach on a match-to-match basis. It might work for a set here and there, or even a couple of matches, but over the long run, it's not going to work. He just doesn't have the speed, footwork and consistency for it.
More worryingly, he can't even play the point construction game he used to do so effortlessly in say, 2006. My biggest frustration with watching Federer against guys like Nadal or Djokovic is knowing he's going to miss first. Whether it's because he pulled the trigger on his forehand but had gotten there a split second later than usual, or his backhand typically breaking down, he's just not consistent enough. The problem is, the same thing is happening against inferior players.
If you look at his vintage performances in the past few years, there are some recurring themes that helped him to those wins. For instance, his 2011 FO win over Djokovic was highlighted by an usually stellar service performance on clay (I say unusual because it's clay), and some otherworldly defense. People forget just how well Roger defended and moved in that match. The other thing that was noteworthy was his backhand. Despite the fact that it missed its fair share of times, Federer had a good idea regarding what he wanted to do with it: use a lot of slices cross court, and change direction by going up the line. The latter in particular, is a shot Federer struggles with mightily nowadays, making his backhand quite predictable, so there's very little risk in going after it if you're his opponent. Meanwhile, the slice is interesting, because while it's a safer shot in the sense that he's not going to miss, it is somewhat harmless on some surfaces (not to mention, useless against someone like Nadal, on any surface). At the AO for example, no matter how good the slice is, the nature of the surface means it's not going to stay low enough. On faster surfaces however, it's a play Federer needs to use more (a la his indoor wins over Del Potro in the past couple of years).
As far as some of his other vintage performances go, almost all of them occurred on faster surfaces. Whether it was the Nadal destruction at the WTF in 2011, the Wimbledon wins over Djokovic and Murray, the Cinci final win over Djokovic, or the wins over Del Potro, all of them came on fast surfaces. Hell, even his first 2 sets in the 2011 US Open semi against Djokovic (which were some of the finest tennis Fed played in the past two years) bore a resemblance to those matches: Federer went after his backhand, attacked the net a lot, used his slice occasionally, and served very well.
The ONLY quality match Fed has produced in the past two years on a slower surface was the Del Potro quarter final at the AO in 2012, and still, that was two years ago, right before a career resurgence. It's difficult to explain why, but for whatever reason, I never gave him a chance against Murray at the AO last year, despite the fact that he pushed it to 5. It just looked like it was an uphill battle. He can't rally with these guys anymore over 5 sets.
He can play clean on occasions, and look like the Fed of old even in longer rallies (ie against Nadal in Cinci last year), but that alone won't be enough. That's why if I were a Fed fan, I'd wait till the second half of the season where we hit the faster surfaces before judging, as I don't think he'll be doing that well elsewhere. For instance, what does he need to do at the AO? How does he need to play? I honestly have no clue. Whereas on grass, it's much more straightforward: Hit through the backhand, even if it misses, use your sliced backhand to set up forehands, and attack the net.
Two shots that I think will be key for Fed's success are the serve and the backhand slice. The latter because it cuts down the unforced errors and allows him to run around his backhand on the subsequent shot, and the former for obvious reasons. Getting free points would relieve him of so much pressure. I'm interesting in seeing how he serves if his back problems are indeed behind him, because that's his only chance at making a run at a major. His serve has been quite crappy for over a year now. Good serving changes things considerably, even on slow surfaces.
But yeah, Hewitt's lobs are class and likewise I hope he gets a decent draw. Just not Federer in kill me please I'm playing like a clown mode 
