The reason Two And a Half Men was such a great series, was that Charlie & Alan had such great chemistry together. They were completely different, and therefore they complimented each other very well. That dynamic just wasn't there with Kutcher Who is otherwise a great actor and comedian as well.
Overall, Two and a Half men stop being the two and a half men when Charlie left.
it was really sad to see the show ending that way, it could've been better but still, even though the finale episode was extremely disappointing, I would still place the show in the top five greatest sitcoms of all time.