I collect a wide variety of die casts and have many CMC's.
I would say detailed wise, they are quite good as some of their models come with over 1,000 components.
"Quality" wise they're not bad either, but there are many other brands who's quality is up to par with them. For example, my latest model is the limited edition Jie Fang CA10, the paint and finish was up to par with the CMC's I have and I paid less than half the price of a CMC. Funny, the CA10 beat out the CMCs with its underbody detail.
I guess CMCs are worth the money, but the only lacking thing about them is a lack of effort for the underbody, which is the case with 95% of the die casts out there.
For true collectors and motorheads, the die cast companies should give decent detail top to bottom.