Well I a quite new around Irrlicht (I haven't even run it for the first time, still downloading) but I have worked with some other (rather sucky, dunno how this one will be) engines, and, depending on where you placed the camera, you could get really nice results or a complete disaster. From your code it seems you placed the camera away from the main guy/object/wathever and it is possible falling outside the level pretty often (this problem happened sometimes with a CD game called Prince of Persia). I migth be wrong in this, or I might not.
That problem seems to happen in many games, especially when you get to the edge of an area( to the guy above my post).and it seems to me, in a portal rendering -type engine...it seems to happen even more........( re: play morrowind for a while........)