I never watched the anime, but the D.Gray-man manga was pretty good for quite a while. I only stopped reading it when the releases became too erratic (I guess it started to feel a bit directionless around the same time). But the concept was cool, the art was nice for a Jump series, it had a good set of characters.... it's a shame how things turned out, really.
As for Clamp, I wish they had stopped working in about 2002, most of what they've done since then has been kind of bad. Honestly, in my mind Tsubasa doesn't even exist. The new Sakura manga is ok so far, but I'm not really sure it was necessary; the original series ended so nicely.