Man, it's hard to type this. My fingernails are worn down to nubs! I've been biting like crazy, watching episodes of Dexter, getting psyched for this killer season's much-anticipated climax (Sunday at 9 p.m. ET, Showtime). Like Dexter's current quarry, the Trinity killer, I've been doing them in threes (and fours), skipping weekly airings in favor of monthly VOD marathons. I've been mainlining the tension till I just can't take it anymore!

Has any season of anything delivered as stunningly as this fourth one in Showtime's serial-killer-of-serial-killers saga? John Lithgow has been a truly harrowing (yet humorous!) match for Michael C. Hall's conflicted avenger -- and the hourly cliffhangers have been shout-out-loud shocking.

Episode 1, anyone? (Car crash.) Episode 4? (Key regular character gunned down.) Episode 9? (She's his daughter?! Are you frickin' kiddin' me?!)

The reveals have been breathtaking as an incognito Dexter has enmeshed himself deeper into the life of upright family man/heartless slaughterer Arthur Mitchell. First it was merely mano a mano between murderers. Then we met the terrorized wife and kids in Arthur's twisted household. Dexter started to see the scary parallels in his and Arthur's daddy issues, spouse deceptions, double lives and born-in-blood backgrounds. I know you're demented, but what am I?

And now Arthur knows who Dexter is. Last week's hour left the two finally face-to-face with all the knowledge they need to make that final smackdown reeeeally messy. The season has snowballed so satisfyingly that this was not only Dexter's highest rated episode ever, but also the most-watched Showtime program of any kind in 10 years (1999's Tyson vs. Norris heavyweight fight).

Last weekend's premiere airing of Dexter's fourth-season penultimate Episode 11 (9 p.m. Dec. 6) drew 2.1 million viewers. Which doesn't sound like much, until you realize Showtime reaches just 16 million households. And many of those, like ours, watch it on delay, either in encore airings (a dozen repeats each week) or via video-on-demand. My Comcast system offers it on VOD in HD (the whole superb season!), so we can watch at our leisure -- as if there is such a thing when Dexter gets going.

John Lithgow has always been a profoundly resourceful actor, and his measured work as monster Mitchell rates special merit for its restraint. Can't believe I'm using that word when the season literally started with him naked in a blood-filled bathtub slashing a woman to death. But with each insane thing Arthur's done, Lithgow's eerie composure has made it yet more chilling. I felt like I'd explode watching that deranged Thanksgiving dinner with Arthur's eggshell-walking family, where Dexter seemed the most "normal" person at the table. Back when Lithgow was rampaging through 3rd Rock from the Sun as an alien ego whose every experience in human form was a crazed revelation, I wrote that he was my comedy god, Now he's my black comedy/drama/thriller god, too.

But he'll have to share that billing with Michael C. Hall. Our ever impressive star turned it up a notch last week as Dexter further imploded with the realizations that he'd killed aninnocent man, thrust his wife and kids into mortal danger, and could wind up just as destructive as Arthur to everyone close to him.

And the show's detractors say Dexter's serial killings have no consequences. Not true. They're just a little deeper-seated than the shows that make it all obvious by the end of the first season, if not first hour.

Hall is hitting us ever harder, four seasons in, as he plumbs the creeping maturity of conscience in Dexter, who began the series claiming he had no emotions, reflection or remorse. The character has lately become a basket case, heartbreakingly coiled and confounded. While creating maximum dramatic impact, he's delivered sharper comedic punch, too. Thanks to the running narration that effectively puts us inside Dexter's head, his ironic commentary and virtual thought-balloon punchlines provide much-needed comic "relief" -- never was the second word of that term so true. They also register the logic through which Dexter allows himself to walk through each day despite his deadly "dark passenger" ride-along.

So Dexter has intensified into not just one of TV's darkest and most delirious dramas but also its funniest. I'd say "one of its funniest," in deference to House, but Dexter now has the Fox drama's character study beat, thanks to Hall's disquieting complexity. House has head and humor appeal, but Dexter gets to your gut.

Disturbing, poignant, resonant, droll -- where does Dexter go from here? I'm feeling like Season 5 might find Dexter trying to go cold turkey from his death-machine addiction. But it could be Dex vs. Deb. Or even -- wait a minute, I'm getting ahead of myself. Sunday's Season 4 finale could put the show on any number of paths.

I'd follow Dexter down all of them.