I think it's good for the same reasons The Office is (or if you don't care for it now, was) so good. It's able to make funny jokes while developing its characters and their nuances. Like the episode last night, it somehow found a way to make a character dealing with post-divorce depression funny. It gives its characters genuine feeling so even when it's not firing on all cylinders, it's still enjoyable. I think it originally got a bad rep for being a bland Office knock-off, but has since come out of that shadow with this solid season.
As for why you don't find it funny - I don't know. Comedy is subjective.
Yup. The characters are great.