It goes up and down in quality. There was a big dip at the start of season 5, then it recovered. The first half of this current season was another serious dip, but now it's back on track again. As sitcoms go, it has some of the most fun characters and relationships I've seen. But it is a shame that the geek humor has been dialed back so much since the early days.
Im on season 6 and the geek humor is still there. I love the episode where they are on their way to the comic con and stop to take some pictures dressed as TNG characters. Its friggin hilarious. I will be on 7 soon so I guess I will see.
It never goes away completely, it's just a lot less than it used to be.