I don't think any WR is worth a top 5 pick, and in general I avoid WRs in the 1st round like the plague. It's just not a position I value highly enough to spend a 1st round pick on, and I feel you can get high quality receivers later on.
Until recently I would have agreed with you and favored bigger, stronger, more physical WRs who could deal with press coverage and were able to block as well. Julio Jones would probably have been my ideal, not that I would use the #6 pick on a WR.
As I've discussed with OTG, and as I discussed briefly in the "Blueprint" thread, with the movement towards the TE-based offense and the integration of the power running game combined with the "Oregonization" of the offense into a more up-tempo approach, I see more of an opportunity for versatile, elusive "flex backs" and receivers who can be moved around to create mismatches, who can create separation in very small windows and accelerate very quickly, and who have the potential to create home run plays at any time. Jeff Demps has that potential, though he's incredibly raw, and he flashed a few glimpses of that in training camp. Percy Harvin is probably the prototype. DeSean Jackson. Randall Cobb. Guys like Tavon Austin and De'Anthony Thomas in college. I think that there's more opportunity to free up those kind of guys when you're playing an up tempo offense and when you have the TEs and the power running game mixed in, and with TEs who can get downfield there's less of a need for big, physical WRs. JMHO. In general, I prefer bigger WRs, but with our offense I think that smaller, quicker guys could present tremendous matchup problems for opposing defenses. Try to match up with the speedsters and we run it down their throats or run over them with the TEs. Try to go big and all it takes is a step for a guy like Austin to be off to the end zone.
I like Roberts. He's similar in size, measurables and style to Randall Cobb, who is one of my favorites. He's a good PR, and has excellent speed and agility (4.40 40, 6.77 3-cone). He's had decent productivity for Arizona despite not having much in the way of QBs. He's not a FA until 2014, so it's too far off to evaluate what his chances are of hitting the open market or what his projected value would be, but he's a nice player.