"And what's with the castings of the motor? It bears almost no similarities to the seemingly higher quality work on the larger 250's."
I agree with Skateparks that the CRF150R frame is less impressively finished than it might be. But apart from the use of ordinary aluminum where magnesium alloy is used on the larger Unicam engines, does anybody who has looked closely at the CRF150R engine find that its castings are lacking in quality in any way?
Though I am hardly an expert, I would say that of the three excellent Unicam engines, the CRF250 is the one with the least apparent quality. The CRF450 and the new CRF150 both use removable camshaft carriers, with very nice die-cast components. The valve cover in these designs more fully surrounds, as opposed to just covering, the valvegear, resulting in better access to the head's internals. The CRF250 design has the valve cover in the same plane as the top surface of the bottom half of the camshaft bearings, which are integral to the cylinder head casting. This was deliberately done by Honda to reduce the number of machining operations, as well as of parts, during manufacture (compared to the CRF450 head) and results in a tighter space in which there are many more sharp edges, burrs, and casting irregularities (like flash) than in the beautifully produced CRF450 cylinder head.
I doubt that these rougher-looking internals of the CRF250 head affect its performance at all. There is no question that it is a fine engine. But if we are discussing the "fit and finish" of mechanical parts, we are making what are essentially aesthetic judgements anyway. I haven't looked inside a CRF150r motor yet, but from the detailed photos Honda has already published (for example, look at the Japanese-only CRF150r Fact Book, at
http://www.honda.co.jp/factbook/motor/crf/200609/004.html ) it seems at least as nicely finished as a CRF450 motor, notwithstanding the lack of expensive magnesium for some of its more visible parts.