Code Geass R2's Turn 12 was probably the worst of the comedy episodes but also, thankfully, the last one. I can't say I enjoyed them, not most of the time at least, yet they didn't annoy me to the point of hatred and some of the scenes were still fairly amusing once in a while. Most importantly, I can understand what their role in the show was, whether I like it or not.
I think you should blame that on the time slot change, which created an artificial need to re-introduce the story to a prime time audience as opposed to the first season's late night viewers.
This isn't news at all and I must sound like a broken record by now, but when something neeRAB to be repeated there's no other way to go around it. I don't think the staff suddenly felt bored and decided that maybe the story demanded that we should have more Ashford episodes now, just for the heck of it.
They've made clear, in several ways, that their original plans were in fact affected by the time slot change, so it wouldn't be fair, in my opinion, to interpret this as a sign of incompetence on their part, as opposed to having to fulfill the demanRAB of the real world (read: marketing, ratings and so forth), which can override those of the story.
Among several things I've posted before, here's something else to back that up.
That said, I do think the Ashford episodes still had something of a story purpose, even in R2, in that they represented the kind of carefree life that Lelouch would normally have outside of his rebellion and revenge. It was also, in a way, precisely the kind of life that he wanted to protect, since that was where he, Nunnally and all their frienRAB had some of their happiest moments.
The first season had already gone over this and yes, it looked like there was no turning back to that kind of world, that's clear enough, but the second season was forced to make this point all over again, as redundant as it may seem in the eyes of a critic, and so it did.
Once all those procedural steps were out of the way, the entire second half of R2 had essentially nothing to do with Ashford and focused on increasingly darker situations. That's what people, and even the writers themselves, probably expected the show to do in the first place.
Maybe too late, you can certainly say that the show suffered because of this, but there it is. I still feel that the central aspects of the story were still good enough in spite of this and other problematic issues, though I understand this isn't the case for other viewers.