I've been listening to some of Louie's "Opie & Anthony" appearances, and he explains on them why he doesn't like to have many recurring characters and why he throws in things that don't gel with the rest of the series. He just enjoys doing things incongruous with everything else in order to foil audience expectations. He's well aware that the Ricky Gervais character didn't "fit the rest of the season" because he didn't do any other "cartoonly stupid characters like that", but that was deliberate.
He even gets off on stuff like that upsetting fans of the show because they don't fit (he also brings up the example of the girl going off in the helicopter). He explained, "If something's not what you're used to, you might find something different to laugh at, and there's nothing better in life[...]the best thing you can do is to find entertainment or humour or intrigue in a location of peoples' minds that they haven't found it before".
I think this stuff is good because it makes the show diverse and unpredictable. It never bothers me. He had another great quote in one of the guest spots about how people have trouble adjusting to things that don't unfold the way they expect. It goes - "[People think] this isn't what I am sure is already good...so I hate it". I think that's an excellent way to explain why people give up on a show quickly because it's too different from what they're used to.
Everyone has shows they like because the show does a certain formula well, but sometimes it's hard to see a show that does things differently and think, "well, maybe I'll end up liking this for different reasons than most stuff I like...maybe it can be good in a different way". It's much easier to decide that a show where things don't work like they do on what you usually like is simply flawed.
I don't mind the offbeat elements of "Louie". The only time the show really frustrates me is when I feel like the points Louie is making are just too obvious or he's repeating himself. This is because I expect more from Louis C.K. as someone who has proven time and time again how creative and insightful he can be. From "Moving" to "Country Drive", I felt the show was becoming derivative and ham-fisted with its messages, but for the rest of seasons 1 and 2, I think it's been consistently stellar, even with the wackier bits thrown in.
I don't see what was so unoriginal about the dentist and doctor bits. Louie said in one of his radio appearances that the dentist bit actually happened to him almost exactly as it did in the show (at least the gas-induced hallucination part) and I've never seen anything like it. The doctor bit wasn't as inspired because it was playing off the Ricky Gervais giggling jackass persona, but I can't say I've seen a doctor like that on television before. Dr. Hibbert on "The Simpsons" did laugh inappropriately at his patients sometimes, but he was never even close to being as obnoxious as the Ricky Gervais doctor. I hate to use a cliché here, but I can't think of a better way to describe this guy than by saying Dr. Ben on "Louie" was like Dr. Hibbert on steroids.