I think the 429 is in response to the short comings of the 427, ie:
Not enough power (is there ever)
Rear cabin needs to be larger
Not certified IFR or true Cat A
Quite a bit of thought has gone in to the 429 and I think it will be successful, especially in the EMS role.
One of the good things about the 427 is it's relatively small size which enables us to land in tight spots close to the incident. The 429 is about the same size just a little taller.
For the pilot the 427 is really nice to fly with a normal cruise of about 125 kts at 85% Tq (100%Tq is Max Cont.) Believe it or not, the pilot seats are very comfortable. Thats right, Bell seats that don't screw up your back! It is very reliable helicopter too, with only the occasional glitch with avionics, and you have the great support from Bell. I enjoy flying it, but I've enjoyed every helicopter type I have flown, which has been a mixture of Robinson, MD, Bell, and Eurocopter.