I tend to agree - he looks to me like he could be the best two-way player in the draft, and he also has great versatility.
In the NBA there is ALWAYS a place for guys who can score, defend and play multiple positions at a high level. That's a pretty rare combination to have.
I think he'll be a very good player, either an All-Star or borderline All-Star.
People compare him to Crowder, but Crowder does not have Johnson's level of athleticism, nor does he have the offensive skill set. Johnson is already a better shooter, ball handler and (probably) defender than Crowder is.
With Johnson, Bradley and Smart wow - that would be a formidable defensive trio. Every one of those three guys can guard at least two positions at a high level.
The key for me offensively is that Johnson can score in multiple ways - he can shoot the three, he has a nice midrange game, he can get to the basket, and he can post on smaller bigs, and he can get to the line. Guys with that type of offensive versatility (Melo, Pierce, Joe Johnson, etc) tend to develop in to very good offensive players.
Combine that with his defensive ability and this kid's potential is through the roof.