I've had both good and horrible mac 'n cheese and I think the difference was the cheese but I remember having that feeling you mentioned. Have you tried different ones? Maybe there's one you'll enjoy.
I tried it twice: first from an ethnic aisle (I'm neither from CA or USA, so this stuff is "ethnic" here - I found it while looking for nori, got curious) and really didn't like it. Then I tried it homemade (I can actually pull out a fairly decent cheese sauce, using Parmesan and Emmenthaler), and the same feeling was there.
Adding some crumbly stuff over it (breadcrumbs and bacon bits, right before grilling/broiling it) improved it a bit, but not enough to avoid that feeling. (I salvaged it by making croquettes out of it. Deep-frying fixes everything.)