Between "Cheers" and "Frasier," Kelsey Grammer spent 20 years playing pompous, erudite, clumsy psychiatrist Frasier Crane. In the history of live-action American primetime television, no one has ever played a character for more years (though "Gunsmoke" star James Arness, who shares the year record with Grammer, played Matt Dillon for many, many more hours). Television is a business where you tend to get typecast by executives and viewers if you play the same character for 3 or 4 years, and where the big stars are usually asked to play a similar character the next time they come up to bat. (Check out Tim Allen as a crankier, meaner Tim Taylor on "Last Man Standing," for instance.)

Given the staggering duration of the Frasier character, it would be easy for Kelsey Grammer to spend the rest of his career playing variations on that theme: Frasier is a librarian! Frasier is an overly-educated auto mechanic! And, in fact, that's more or less what he did after "Frasier" ended, first with "Back to You" (Frasier is a local TV news anchor!) and then "Hank" (Frasier is a destitute ex-CEO!), both of them canceled after a single season.

With "Boss," the new Starz drama that debuts Friday night at 10, no one will be having the Frasier is the mayor of Chicago! reaction. Same man, same familiar face and stentorian voice, but the performance and show are worlds removed from the role that made him rich, famous and a four-time Emmy winner.

And in this case, that's a very good thing.

Grammer plays Tom Kane, the doubly-buttressed man in charge of the Chicago political machine. He's been mayor forever, and his wife Meredith (Connie Nielsen) is daughter of one of his most celebrated predecessors. He controls the necessary votes on the city council. He gets to more or less handpick who will win the gubernatorial primary. He is a gifted orator (as you would expect any Kelsey Grammer character to be), a smooth deal maker and, when he needs to be, a terrifying bully.

He is at the height of his powers.

He will be dead in less than five years.

"Boss," created by Farhad Safinia, actually starts with the latter point, as we meet Kane at the moment he's being diagnosed with Lewy Body, a form of dementia that also has symptoms in common with Parkinson's. Within a few years, the doctor tells him - if not sooner - he will lose control of his body, and his mind, and the most powerful man in Chicago will be a prisoner of his own disease, and then dead not long after.

And, based on the three hours of "Boss" that I've seen, Tom Kane is not the type to go gentle into that good night.

When I first saw a trailer for "Boss," it almost struck me as a kind of Cable Drama 101 template: veteran actor looking to change his image, central character who changes their life after a fatal diagnosis (which they usually keep secret), familiar genre story told in a rawer fashion, etc. And certainly all of those elements are present in the finished version. But knowing the broad strokes didn't entirely prepare me for the intensity and magnetism of Grammer's performance. I knew the man gave good speech, that he was a classically-trained dramatic actor who accidentally became a sitcom star, and that whenever the "Cheers" or "Frasier" writers gave him a more serious moment, he played the hell out of it, but I still wound up thunderstruck by the actual work.

The premiere episode was directed by Gus Van Sant, and Van Sant makes sure that the first - and for a long time, only - thing we see is Grammer's face as Kane gets the brutal diagnosis. His face remains stone-like and resolute, and yet if you focus on his eyes, you can see so much information being absorbed, processed, debated, and settled. There are a lot of moments in "Boss" like that, where the camera just sits on Grammer's face, whether Kane's delivering a speech or listening to one, and you don't want to be looking anywhere else.

There are, in fact, a lot of speeches on this show, where at times it feels like the script has no dialogue and lots of monologues. Many of those speeches are terrific - especially those delivered by Grammer -  but there's a definite sense of overkill after a point. When one of Kane's goons goes to threaten a doctor, he has to first deliver a speech about the Hippocratic oath; when a political flunky has a point to make to an underling, he dresses it up in a lecture about the evolution of golfing attire.

For that matter, less-is-more might also be wise with the various visual flourishes that Van Sant introduces, and that are adopted by the later episode directors. Van Sant goes for a very intimate approach, lingering on faces and even parts of faces (he's very fond of eyeballs, for instance) in particularly emotional moments. But while some of those touches work splendidly at times, as with the speeches, it eventually feels like "Boss" is trying too hard to both impress and make you recognize how significant something is. It's underlining the emotion and then covering it with yellow highlighter, and after a point it becomes a distraction, with the editing choices pulling you out of the moment and reminding you that you're watching Important Art. It's particularly noticeable in any scene involving Kane's estranged daughter Emma (Hannah Ware) as she works at an inner-city medical clinic and is drawn to a patient's drug-dealing nephew. (Or maybe it's that those scenes are over-edited to compensate for a flat performance.)

"Boss" also suffers a bit for having to remind people that they're watching a pay cable drama, with nudity and/or sex scenes so gratuitous as to be laughable. A lot of similar dramas do very interesting, character-revealing things with those kinds of flesh-baring moments (just check out the dysfunctional sex life of Damian Lewis' character on Showtime's excellent "Homeland"), but mostly on "Boss," they seem to be there because it's expected on the home of "Spartacus."

The thing I wonder the most about "Boss" is how necessary the Lewy Body story is. On the one hand, the diagnosis is an inciting incident, something that forces Kane to change how he conducts business, and something that adds tension to ordinary scenes (say, when his hand begins to tremble during a council meeting). On the other, the story of the perfectly healthy, powerful boss of a corrupt machine, played so well by Grammer - and surrounded by an interesting supporting cast that includes Martin Donovan and Kathleen Robertson as Kane's top aides, Troy Garity as an investigative reporter and Jeff Hephner as Kane's hand-picked gubernatorial candidate - feels like plenty to generate drama on its own.

Tom Kane often runs into trouble because he's trying to do too many things at once, and while "Boss" is a very promising drama with a great lead performance, it might be better off easing up a bit and just letting viewers appreciate Grammer's career-redefining work.

Alan Sepinwall may be reached at sepinwall@hitfix.com