Is it just me, or starting season 3 and through the end of the show, they made the Denise character more dumb, and irrisponsible? Could they have done this because of the detering relationship between Bill and Lisa?

Personally I liked the way the character was handled. This can happen in real life where a student was a straight A in high school and only goes to college to please family but does not want to be there and/or finding it more difficult to handle. I just did not like the flakyness that progressed each season. Her dealing with finding herself and searching for identity is very realistic.