He's a very talented actor, I'll give him that, no question, but greatest actor of our time? Ehhhh, I don't know about that. There have been many actors already named in this thread, as well as a number of others who I have not seen yet, that are just as talented, and more then a few who are more so.
Just to throw out a few names here:
Willem Dafoe
Patrick Stewart
Gary Oldman
Laurence Fishburne
John Malkovitch
Morgan Freeman
Robert Downey Jr.
Hugh Jackman
Denziel Washington
Kelsey Grammar
Leonardo DiCaprio (from Catch Me If You Can onward)
also gonna bump Christopher Walken, Laim Nesson, Michael Keaton, Heath Ledger, Philip Seymor-Hoffman and Daniel Day-Lewis
Seriously, there are a lot of actors out there of genius level acting talent that have just not attained the near-ubiquitous pop culture phenomena status of Johnny Depp