After weeks of hit-or-miss guest judges - hits: Neil Patrick Harris, Katy Perry; misses: Avril Lavigne, Victoria Beckham - Ellen DeGeneres finally makes her debut on American Idol tonight, as the aspiring pop stars who survived the show's hodge-podge audition episodes make their way to Hollywood for the next round.

DeGeneres joins TV's most-watched program at one of its most critical junctures, just weeks after its undisputed star, Simon Cowell, announced that this will be his last season as its pithy voice of reason/scorn. (He will be importing his hugely successful British talent show The X Factor to Fox this fall.)

Until Cowell, ever the spotlight hog, drew all the attention back to him with last month's announcement of his impending departure, the biggest question surrounding American Idol this season was if DeGeneres could replace Paula Abdul - who left the show in the off-season after failing to reach a new contract agreement - at the judges' table alongside incumbents Cowell, Randy Jackson and Kara DioGuardi.

I don't think it will be that easy for Ellen. I might be in the minority here, but I loved everything about Abdul on American Idol: her non

sequitur-laced critiques, her weather-vane-in-a-hurricane emotional swings, her good-natured ability to be Cowell's punchline-punching bag, her ability to find a silver lining in even the most black cloud-like performers; she was the kind of good-natured train wreck that any reality series would kill to have on board. (I couldn't have been less surprised at reports that Cowell is considering Abdul to be a judge on The X Factor; despite detractors of his musical acumen, Cowell definitely understands the basic mechanics of compelling TV.)

Unlike Paula's seemingly natural loopiness, DeGeneres's brand of comedic befuddlement is far more studied. Despite her astonishingly successful career - hit sitcom and talk show, best-selling book and comedy CD/DVD, well-received turns hosting the Emmys and Oscars - I've never been a fan of her stammering, seemingly stream-of-consciousness shtick.

Depending on how charitable one is feeling, DeGeneres's act is either a spot-on homage to or outright rip-off of Bob Newhart's entire comedic persona. (Although if her fawning daily talk show is any indication, she will have no problem filling Abdul's pumps as the designated cheerleader at the Idol judges' table.)

However, I will defend DeGeneres against one of the more ludicrous criticisms levelled against her since news broke that she'd be joining the show: that her lack of a musical background will somehow damage American Idol's credibility.

First, with apologies to fans of such Abdul non-classics as Straight Up, Cold Hearted Snake and Opposites Attract, the woman DeGeneres is replacing is not exactly Aretha Franklin. And second, can any show that has foisted finalists as unfortunate as Justin Guarini, Taylor Hicks and Blake Lewis onto the record-buying public possibly have any musical credibility left to damage?

In any case, the question facing DeGeneres has less to do with her ability to replace Abdul than whether she will even stick around after this season. In an interview with Entertainment Weekly in December, as rumours of Cowell's departure began to swirl, Ellen stated, point blank: "If Simon goes, I go! ... I will not be there without Simon."

Now, that might have just been public posturing, a last-ditch effort to pressure Cowell to stay in the Idol fold, but it was more likely DeGeneres acknowledging the inconvenient - for Fox, at least - truth: Abdul might be replaceable; Cowell isn't.

No matter who is tabbed to take his chair next year - and the names bandied about include record industry execs Tommy Mottola, Jimmy Iovine and Guy Oseary - expect the show to suffer a precipitous drop in ratings. However, Fox will be able to assuage itself with the fact that The X Factor will be a surefire smash.

(A brief aside here regarding the New York Post's Page Six report last week that Sirius XM satellite radio host Howard Stern will replace Cowell next season: this will never happen. Stern is far too polarizing and controversial a figure for American Idol, the definition of "mainstream" circa 2010.)

No matter how it all shakes out, DeGeneres's debut tonight will be a key moment in what threatens to be the most intriguing season of American Idol yet - even if most of that intrigue will play out far from the caterwauling on screen.

American Idol airs tonight at 8 on Fox and CTV.

bboshra@thegazette.canwest.com