Well this was a trip down the memory lane. I built a small game on Irrlicht at the time and I remember these discussions also.

Irrlicht had its editor (irrEdit), a sound system (irrKlang), and some basic collision detection and FPS controller was built right into the engine. This was enough to get you a considerable way through a fully featured tech demo, at the very least. (I even remember Irrlicht including a beautiful first-person tech demo of traversing a large BSP-partitioned castle level.)

However, for those not afraid to stitch these additional parts from other promising libraries (or derive them from first principles, as was fashionable), OGRE offered more raw rendering prowess: a working deferred shading system (this was the heyday of deferred shading), a pop-less terrain implementation with texture splatting, and more impressive shader and rendering pipeline support, with the Cg multi-platform shading language. I remember a fairly impressive ocean surface and Fresnel refraction/reflection demos from OGRE at the time.