I thought I'd post my thoughts on this class since I usually enjoy playing the "tank" in RPGs.
Unlike the other classes there isn't really a good real-world example to base the dreadnought off of; therefore I think a good design is going to be critical in order to keep him from seeming anachronistic and generic compared to the other classes.
At low levels the dreadnought might be comparable to a street thug or the like. Higher levels might see him develop into sort of a melee shock trooper. Basically, I think it will be important to keep the dreadnought from looking like a medieval knight- but not so advanced as to look robotic.
I like the fact that even though this character is a front-liner, he ont be limited to melee only weapons, however I think you have an opportunity to create some interesting steam-punk melee weapons. At lower levels things like clubs, night-sticks, and sabres will do, but more advanced weapons might include electric cattle prod-type weapons, chain swords, and pneumatic hammers (sort of like jackhammers maybe).
Heres a sketch to suggest how the class might progress-
http://img.villagephotos.com/p/2004-9/826976/dreadnaughts.jpg welp, hopefully you might find something interesting among that ranting
