It's true: the old ones are very good, the recent additions to the Ender series for instance are terrible, they're an obvious cash in on his brand, I suspect he writes them quickly so he can make some quick cash (or to fill up his existing publishing contract.) and spends the rest of the time on stuff that doesn't suck so hard.

A review I read of his recent story collection said his recent stories didn't have to try so hard, he knew they'd get published and he was more or less keeping a hand in, his earlier work he's working hard and striving for quality, this applies in spades to the rest of his recent work and may well apply to any entity's (sometime) fall-off in effort or innovation after they've succeeded.