Harry Morgan did a great job, and his character was a nice addition. There was one episode in particular, where he was the sole remaining live member of his former unit, and gave a toast to his deceased friends, that jumps out to me. There was just something special about the Henry character, though. He was the glue of the show.
The political agenda was obvious. Even Larry Linville, in an interview after he left, criticized the direction the show was heading. Like many great comedies, the producers and writers forgot what made the show great in the first place. I kept watching - and the show continued to have a huge following - but, if we're being honest with ourselves, M*A*S*H was basically crap the last 5 seasons or so.
What I do nowadays is pay attention to the opening credits. As the helicopter is flying in, if the background is hazy, I watch it. If it's clear, I switch the channel.