It depends.
Getting ahold of him is one thing. Whether or not he could be a viable receiver in this system is an altogether different question. Many players with great athletic ability simply cannot function to their previous level when put into a different system, different coaches, etc.
It is my own opinion (and nothing more) that a player's success on the field is much more than is own ability. It's how he can function in his environment. Understanding the playbook is one thing, but also grasping the philosophy behind it is another. Being able to work well with his teammates, both on the field, in the classroom and in the locker room.
There is so much more than just a player's proven abilities with one team. Sure, guys like Randy Moss can come into New England and function at a VERY high level, even thrive, but Randy ws also incredibly smart vis-a-vis football knowledge. We thought that Chad Johnson would be a great addition, but look how he turned out. New England wasn't Cincinnatti, and it showed.
So maybe Calvin Johnson comes in and plays like his hair is on fire, or maybe he plays like he's in a haze. Regardless, that's an awful lot of money to tie up without some serious due diligence on behalf of the Patriots front office.
Just my 2-cent's worth.