I have a carbon 15 and I enjoy it. It is a bit on the steep side when you think about it. I paid little over $1,000 after all fees and taxes for my carbon 15 (and I know people building OLL for less than $700.
If you don't want to go all through the million of options of building a OLL, the carbon isn't a bad choice. I just think of it more of a Toy than an actual AR. Both my Military and LE friends love playing with it. It's very lightweight compared to the standard AR and shoots just aswell. Only thing I don't like about it is there is no Dust Cover ( I like that piece of mined of keeping my chamber clean and clear).
Overall I'm happy with mine. I have over a 1,000 rounds with really no FTE or FTF. In the long run I'm going to probably change out the barrel and make it to a nice varminter.