Honestly, I think Abby was a redo of Lucy as far as far as introductions. I didn't remember the season five premiere, so I watched it last week on Pop. Her intro is horrid, especially when you remember it with S4's cliffhanger ending.
I feel bad for Kellie Martin because she could have worked on this show had she joined later in the show's run. It was really bad timing personally for her. That'll always be a big "what if" for me.
I also watched Doug's exit last week, which I hadn't seen in YEARS. I always managed to miss it. Good grief, his selfishness is off the charts. I was glad Carol called him out on it. I also hate that they made her pregnant after Doug left. It made Doug look like a deadbeat asshole. Also, who tells someone they're going to be pregnant by FAX??? I have never heard of a person giving someone their fax number as a way to get in touch with them.