The Sheen and Cryer characters are stuck between two amoral poles -- their awful mother and Alan's surprisingly awful son. (Credit to the creators for making a pre-pub kid so unappealing on a prime-time show.) They're also stuck with each other.
Alan is very aware that he's stuck, and complains about it all the time. Now, if he were the only lead, this show might be as bad at "The War at Home" -- all kvetching. But Charlie's main goal in life is to rise above -- or, to use Mel Brooks' phrase, rise below -- his problems. He's very comfortable ignoring and even exploiting those problems -- like using a gig as Alan's receptionist as an opportunity to turn his brother's chiropractic business (boring!) into a massage parlor. And he usually gets away with it.
What's most appealing about Charlie is that he obviously cares about his family but, also obviously, he determined long ago not to let them bring him down. Thus, the episodes rarely culminate in maudlin lesson-learning resolutions; while Alan works his way into a frenzy, Charlie works his way back to his own lazy horn-dog stasis.
Such moral purity is rare on network television. I can't think of another sitcom character that works quite the same way. It's as if Maynard G. Krebs became fully self-actualized and took over "The Many Loves of Dobie Gillis."
Not bad points, and I think the presence of Charlie Sheen, Jon Cryer and Holland Taylor puts this show a cut above most sitcom casts. Ultimately, though, I think the show is done in by its glacial pacing and staging, with talking-head characters standing around and delivering punchlines. Put it this way: if you're going to do a show with such unappealing characters, you'd better make it move as fast as "Seinfeld" did so we don't have time to focus on their general unappealingness.
At least it's an improvement over creator Chuck Lorre's previous show, "Dharma and Greg." That was a show where the supposed star -- Dharma, as played by Jenna Elfman -- was a complete obnoxious horrible freak, and none of the writers seemed to be aware of this, so they kept writing the show as if we were supposed to find her cute and charming. (There's one thing worse than an unappealing lead, and that's an unappealing lead who's supposed to be appealing.) The frustrating thing about that show was that it had two great characters: Greg's rich parents, played by Mitch Ryan and Susan Sullivan. If they'd spun those characters off, they might have had something.