I like the first book. Childredn and messiah were also good.
Everything since those three has basically smacked of flogging the money horse despite having killed it, beat it for a while, raised it as a zombie, flogged the zombie until it fell over again, and then carried on for good measure for a while longer so as to extract the maximum amount of money.
I have no clue as to their quality, but I just haven't bothered to read them purely because of the sheer volume, the lack of time, and the being told by people whose opinions I trust that they basically suck.