Wall is a tough player to evaluate. On the one hand, he looks pretty excellent by PER when you consider his age. A 21 year old point guard putting up close to an 18 PER is very promising.
On the other hand, his Offensive Rating (points produced per 100 possessions) is 99, which is pretty abysmal.
The issue is his turnover rate and shooting efficiency. A major flaw with PER is that you can "overcome" lesser shooting efficiency by taking quite a few shots and end up with a decent PER (assuming you do other things, which Wall does...he has a very strong Assist Rate and rebounds pretty well for a point guard). However, others believe that shooting efficiency and turnovers destroy offensive effectiveness, which is reflected in his Offensive Rating.
Right now, I'd say that Wall is probably mediocre in overall effectiveness but is a very volatile asset going forward...he could settle into a decent but quite overrated player ala Rudy Gay or he could find ways to mitigate his turnovers and shooting efficiency and become more of a Rondo (offensively...nothing suggests he'll ever be a defensive dynamo). The fact that he does one incredibly important thing (create for others) extremely well means that he does have the potential to be a very valuable player. On the other hand, we've seen what elite ability to create for others paired with nothing else did for Sergio Rodriguez. Wall will really have to learn to be efficient as a scorer and bring his turnovers down.
I don't see any evidence, though, of Wall being selfish and he doesn't look it when I watch him. He definitely has a point guard mentality.