the other thing you need to remember about any software(especially libraries or engines like this) is this; the best software is what i'd call "elegant". something is not elegant because there is nothing to ADD, it is elegant because there is nothing that needs to be taken AWAY. irrlicht provides a simple, elegant, and effective interface to all the features it does provide, without having any of the needless complexity many other engines involve.
adding features is only a matter of time, but the part of the DESIGN of an engine that is most important IS the API. and at this Irrlicht (for me anyways) far and away outpaces every other engine i have had experience with. therefore from my perspective i can conclude that irrlicht is most certainly NOT design broken, it simply has a few desireable features missing
(many of which ARE being developed as we speak)
here is a short list of engines i have used(rather a large number i think):
neoengine
ogre
crystal space
quake3
quake2
genesis3d
my own(OGL/GLUT based, developed during a 3d gfx course in college)
so i am basing this on something, all anyone can base anything on, experience
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~Ted