Fans were psyched when Ellen DeGeneres was appointed an "American Idol" judge: Who better to replace the relentlessly sweet, clearly-scripted Paula Abdul than Ellen, a tart and spontaneous wise-girl? But a month after Degeneres' debut, critics have given her a lukewarm response, and there's even a Facebook campaign to get rid of her. Where is she going wrong? Five theories:

1. Ellen's invisible
Ellen is so anonymous on American Idol, she's "in danger of almost disappearing entirely," says Mary McNamara in the LA Times. There's almost no sign of the "ambition and chutzpah" that made Ellen an Emmy-winning, Oscar-hosting "force to be reckoned with." Maybe it's the overbearing influence of fellow judge Simon Cowell, who is in particularly "disgruntled form" this season.

2. She offers no more insight than a typical viewer
Ellen wasn't hired to be the "voice of the voter," says Robert Bianco in USA Today. America wants to hear from her because she's an "incredibly successful TV star" who "knows more than most about performing in public." Where's that Ellen?

3. She's simply too nice
Ellen's decided her job is to deliver "good news" to wannabe singers, says James Poniewozik in Time. But "that ain't all there is to Idol." We watch the show for its withering put-downs, too. Ellen doesn't have to go for the full Cowell, but, at some point, she'll have to "get [her] hands dirty" and "tell somebody that their dream just is not going to come true."

4. She's nervous
This isn't the Ellen we know and love, says EW's Michael Slezak, quoted on CNN. Though she's clearly able to deliver a "strong point of view," she's been "tentative" and even "apologetic" so far. "She just needs to own it" — and she better start fast.

5. She hates Simon
Ellen's performance has been worsened by a spat with the famously acerbic Cowell, suggests gossip-site TMZ. They "flat out don’t get along." Producers have even "separated the two" between takes — but things have "only got worse." Luckily, Cowell is leaving after this season.