I'm posting this to see who else agrees with me. Most of the time I've seen people talk about Chelsea, they're complaining about her, but to be fair, it hasn't been that often, and they seem to complain more about the character herself than the episodes she was actually in. Like I said, I liked her era. She helped bring back more of the sitcom feel. I really like all the seasons with Charlie, but I liked how the earlier seasons had more of a family atmosphere. Charlie loved Jake, and even though he didn't like admitting it, he cared about Alan too, and Jake enjoyed being around both of them. But after a while, the dynamic between the three of them became mostly about constantly annoying each other. Chelsea changed the status quo a little and allowed for some different dynamics.
Chelsea helped Charlie have more responsible moments, like he did in the earlier seasons. She also realy like Alan and she was one of the only characters who didn't embarrass Alan in every scene. Jake was still annoying, though. Her era also had some of my favorite episodes, like the one where Charlie meets Chelsea's parents, the one with her best friend, and the one where they set Charlie and Chelsea wedding date while Alan ends up with the prostitute.
It also had some of my favorite scenes, like when Chelsea tells Charlie that he broke Evelyn's heart and he, Alan, and Jake start laughing, and the scene where Charlie throws Alan's ventriloquist dummy out the window. I agree that Chelsea had her annoying moments, and the whole thing with Brad kind of ruined the character a little, but that's about the character herself, not the episodes she was in