Through it all, 'ER' won her heart

Characters like Maura Tierney's Abby (left) made ''ER'' - which begins its last and 15th season tonight - a favorite. (Danny Field/NBC)

When "ER" begins its final season tonight at 10 on NBC, I will be where I have been most fall Thursdays at that hour since 1994: parked on my couch, engrossed in the soapy goings-on in the Cook County General emergency room and hoping I don't share any symptoms with that episode's patients.

Over the course of its 15-year run and umpteen cast changes, the show may have fallen out of favor with many viewers, Emmy voters, and TV critics, but I've never been able to kick the habit.

Like most long-term relationships, my love affair with the long-running medical drama hasn't always been perfect. After the giddy high of that first season, when we were both still young and George Clooney was just starting to work his head-down, eyebrows-up magic, the show settled into familiar patterns, and the passion waxed and waned like a ventilator.

Sometimes things got messy - explosions, hostage takings, ill-conceived love affairs - and I was embarrassed by my devotion. Occasionally I was tempted by something new and shiny. Most significantly I ran off to whoop it up with my friends at "Lost" when ABC moved the island to 10 on Thursdays. There was no way another out-of-control whirlybird story line could compete with an exotic smoke monster, intricate plotting, and the testosterone-fueled firepower of Naveen Andrews and Josh Holloway.

I may have been unfaithful, but I never abandoned "ER" completely. I would just slink back to it on VHS or in my DVR, admittedly on a night when I had nothing better to do than listen distractedly to the same old stories while I paid the bills or folded the laundry.

"ER" came to the small screen with a lofty pedigree. The pilot script sprang from the mind of novelist and former medical student Michael Crichton ("Jurassic Park") and was produced by Steven Spielberg. Cast with mostly unknowns ("Top Gun"/"Revenge of the Nerds" star Anthony Edwards excepted), the series debuted to rave reviews and created an instant star out of the previously struggling Clooney.

What made the show special was its breakneck pace and ability to show doctors navigating between their intense work and equally intense private lives. During its run the series has earned more Emmy nominations - a hefty 122 - than any other show.

Alas, times changed and my devotion to "ER" got more exclusive. As the original stars exited through those ambulance-bay doors, fewer viewers tuned in. But I kept defending the show's dependability and flashes of brilliance.

Somewhere around season 6, "ER" began to put on weight - to be fair so did I - taking on cast members with varying degrees of charm. Some, I loved. (Hello Goran Visnjic as sexy-yet-tortured Croatian medicine man Dr. Luka Kovac!) Some I was happy to see stabbed. (Goodbye Kellie Martin as incredibly irritating medical student Lucy Knight!) Some, like Linda Cardellini's nurse Sam Taggart, brought youth and attitude. Some, like John Leguizamo's Victor Clemente, brought the crazy.

Through the years the show took me for granted, recycling plotlines as if I wouldn't notice. (Another prickly ER chief? Really?) It also tried to shock me into paying attention with increasingly naked bids to ignite the original spark. But no matter how many times the ER blew up, I returned to see how they would pick up the pieces.

But by season 11, I'll be honest, I was just going through the motions. And when young doctors Neela and Gallant married, Gallant shipped off to war, returned for a minute and then was killed - well I'm not sure I ever fully forgave the writers.

Yet there I was, watching all of those breathlessly promoted "most dramatic" or "most powerful" episodes. Mainly because every season had a fresh or affecting story line, the return of a familiar face, or strong guest-star performance from the likes of Ray Liotta, Forest Whitaker, or John Mahoney.

In truth, the main reason I stayed was Maura Tierney. As we watched her go from Nurse Abby to Dr. Lockhart, climb on and fall off the wagon, and get in and out of bed with Luka, Carter, Luka again, and Stanley Tucci's Dr. Moretti, Tierney turned in a fierce, committed performance that was always grounded in reality even when the show wasn't.

She nailed the messy life of a working mother in a difficult relationship with her husband, peers, and alcohol. That Tierney never won an Emmy will be the series' most unfortunate postscript.

Tierney is saying her goodbyes early in this 19-episode final season, but I'll keep watching until the end. Some of the old characters are returning for a swan song, while a few new ones check in. (Next up: Angela Bassett as this season's, you guessed it, prickly ER chief.)

From "M*A*S*H" to "Quincy" to "Scrubs" to "House," I've always enjoyed a medical mystery on TV. But with "ER," in particular, I appreciated why so many different kinds of people feel a calling to medicine. (It also helped provide insight into my mother's job as a nurse.) Even when the show hit rough patches, the staff at County General could be counted on to try and make us feel better.

After 15 seasons I can't stop watching until the show flatlines forever.

Sarah Rodman can be reached at srodman@globe.com.