Jimmy Fallon is doing well and has been doing well, and he is just generally a fairly funny comedian that is adept at these sorts of things. More importantly, Jimmy Fallon actually has a really solid fan base that is already built in from his other work, and people are watching.
I watched the first episode of him as host of the Tonight show. I found him to be a little funny, but mostly boring and exceedingly lame. Since this is the formula that made Jay Leno such a hit in the show, I'm sure Fallon will do just as well.
Fallon has had a history of success in entertaining, starting with his days at Saturday Night Live. His choice to replace Conan O'Brien was controversial, but he ended up being a very funny and popular replacement, which is proven by his choice to fill Jay Leno's vacancy. Additionally, the Tonight Show is a staple of late night television and has been for many decades dating back to Johnny Carson. Fallon's past success and the inherent popularity of The Tonight Show signify that Fallon will succeed as the new host of The Tonight Show.
I believe that Jimmy Fallon will do great as the new host of The Tonight Show. NBC wanted some new blood in the time slot and I think that he delivers in that area. Jay Leno's older fans might need to take a while to adjust, but I think they will get used to Jimmy and enjoy his show.
Jimmy Fallon is funny, but not nearly funny enough to replace Leno on the Tonight Show. Conan O'Brien was the right man for that job but NBC really screwed up the Leno/Conan situation. In my opinion The Tonight Show will never be what it used to be and you'll have many networks competing for the top spot in late night tv with no clear winner for many years to come.