The MT90 has been a stalwart shoe in Shimano's range for many years now, and I'm basing my comments here not just on the new pair I've had to test but my long-suffering three-and-a-half year old pair that have been pressed into service for pretty much every type of riding I can think of, save for road racing.
These mountain bike/touring shoes came into the road.cc offices a couple of weeks ago and they've pretty much been on my feet ever since. So far my feet aren't complaining.
The dual pivot callipers have a modified arch which, Shimano say, gives you a more linear response. Possibly – although you’d have to run them alongside the old model and concentrate really hard to notice much difference there. More significant is the brake block compound that provides significantly stronger power in both wet and dry conditions with a single trigger finger, giving you the confidence to ride faster into bends and brake later.