'American Idol' matters. No, seriously!

American Idol (7pm Tue and Wed, Fox)

I used to be American Idol’s biggest fan, but by now most of us know it’s jumped the shark. After a string of bland winners — Kris Allen, Lee DeWyze, Scotty McCreery — we realize that the show will most likely disappoint us after its long process of sifting and winnowing. The young singers will play-act toughness or sexiness or vulnerability, bringing nothing new to songs by Marvin Gaye or Sam Cooke. Viewership has dropped by 30 percent this year, so clearly the secret is out.

The only people who haven’t gotten the message are the judges and host Ryan Seacrest. They remain in a perpetual state of awe about their run-of-the-mill contestants, with no blunt Simon Cowell on hand to provide a reality check. “One of your Idols will soon become music royalty!” Ryan crows, seeming to believe what he’s saying. Jennifer Lopez regularly shows us her goosebumps after a ho-hum performance, and Steven Tyler is so impressed by the singers that he’s run out of superlatives. Instead, he blurts out superlatives that don’t make any sense: “Your voice just climbs inside of everyone and changes them for that moment!”

The thing is, Seacrest and the judges have become so lovable (another byproduct of Cowell’s departure) that you hate to see them disappointed. I’m inclined to pretend I’m excited about the season finale, just for their sake. So come on, everybody! Let’s tune in and (wink, wink) watch one of our Idols become music royalty!

Masterpiece Mystery (8pm Sun, PBS)

I’ve been telling you to watch the brilliant second season of Sherlock with an increasing sense of urgency. This week’s installment is the season finale, and … YOU HAVE TO WATCH IT! It’s among the most compelling TV episodes of 2011-12.

The 21st century version of Sherlock Holmes, played with crazed intensity by Benedict Cumberbatch, matches wits with his evil counterpart, Jim Moriarty (Andrew Scott). This is truly a smackdown for the ages. Moriarty and Holmes are both arrogant Übermensch types bored by ordinary people; only when pitted against one another do their computer-grade minds fully engage. True to form, Moriarty hatches a plot to destroy Holmes that leaves the detective — and us — stupefied by its diabolical mechanism.

I don’t want to tell you anything else about the plot, except to say that it’s the ultimate test of Sherlock’s deductive powers, not to mention his humanity. And if you recall, his humanity has been in doubt for the last few episodes.

I’ll also reveal that the season ends with a doozy of a mystery for us viewers to solve. That’s right — we get to play Sherlock Holmes ourselves until Season 3 comes around. My brain hurts already.

Mrs. Eastwood & Company (9pm Sun, E!)