Easily the most established name of the four, Jamie Bell is also the most surprisingly out-there piece of casting (Jordan has been rumoured for long enough that fans have already had plenty of chance to debate the possibility of a black Human Torch). Much of this opinion is based on the way that many still associate Bell with his star making turn as northern ballet prodigy Billy Elliot.
Since that time, though, Bell, who is still just the same age as Teller and Jordan, has gained ample experience of blockbuster filmmaking on a big scale with leading directors like Peter Jackson on King Kong and Steven Spielberg on The Adventures of Tintin. Using performance capture for the whole of the latter production, Bell has proved himself completely capable and comfortable with the kind of technology that is likely to encase him in The Thing's rocky skin.
Kinberg, The Fantastic Four's writer, has also penned X-Men: First Class and therefore has a reasonable say in Fox's shared superhero universe. It is his previous collaboration with Bell that has probably scored the British actor his role in Fantastic Four. The Kinberg scripted teleportation actioner Jumper may have received mixed to poor reviews, but Bell's superpowered renegade was easily the best thing in it.
Is he a good fit?
To be honest, Bell's casting is a bit of a strange one. While most of the team are made up of brainy science types, Ben Grimm is very much the muscle (even before his transformation into the tough, craggy Thing). In the original storyline Ben was a tough streetwise kid from a rough part of New York who grew up to be a high school football star and, later, a US Marine. He meets and befriends Reed in college and agrees to fly his spaceship once he becomes a military test pilot.
The Ultimates version has Ben and Reed as childhood friends and the former using his more physical attributes to protect the brainy latter from bullies. In this storyline, Ben needs Reed's help with his maths and science homework and his lack of science knowledge allows him to be the recipient of useful exposition for the audience. Either way, the character is physically large, tough and known for his gravelly voice and gruff demeanour.
While Bell is undoubtedly a talented actor and, given his Tintin experience, would probably be able to perform well in a motion capture suit when Ben is transformed into the Thing, it is hard to imagine him embodying a big, solid, lovable lunk in the pre-transformation scenes or being able to find quite the right voice for the role. The Shield's Michael Chiklis was one of the few performers that emerged creditably from the original movies, perhaps this will be one area where the reboot fails to match them.
Having said that, there have been plenty of comic book movie castings just as unexpected in the past that have worked out well, so perhaps we'll just have to wait until next summer to see the success of Fantastic Four's bold casting choices.