Over the second half of last season, Grey's Anatomy went from being the TV pal with whom every get-together feels like a giddy first date, to something more along the lines of a house guest who constantly gets on your nerves.

That's the assessment of the Contra Costa Times, and while it may seem a hit harsh, there's no doubt that many fans grew frustrated in Season 3.

The same with the cast members, who squabbled over the Isaiah Washington situation off screen, while on screen, a dark cloud hung over SGH.

Death, destruction and personal devastation reigned.

And oh, those creative missteps: Best pals George O'Malley (T.R. Knight) and Izzie Stevens (Katherine Heigl) making booty calls? Ugh.

By the time the season of discontent was over, two key cast members were gone �" Washington and Kate Walsh, whose spin-off series, Private Practice, debuts tonight.

Gone, too, was much of the good will the show had built up.

As Grey's Anatomy returns for its fourth season tomorrow on ABC, its vital signs are strong, but still we wonder: Can this show get back to being the funny, frothy, intoxicating guilty pleasure it once was?

Fortunately, creator Shonda Rhimes is saying all the right things: It's time to lighten up, sex it up and have a blast!

"I came back to this season sort of mandating that we have a lot of fun," she told TV writers this summer. "I felt like Season 3 was a dark season. It just is. I mean, Meredith's (Ellen Pompeo) mom dies. George's dad dies. Meredith's stepmother dies. It was a bloodbath. But I want to get back to us enjoying it and having fun."

Still, Shonda Rhimes by no means cops to creative mismanagement.

While she admits the behind-the-scenes drama of last season was difficult, she stands by the direction of the show's storytelling: "It felt like the journey these characters needed to take" - and even the George and Izzie plotline.

"I understand it," she says of negative reaction to the unexpected couple. "I think, when Meredith and Cristina (Sandra Oh) and Alex (Justin Chambers) find out, they are going to have some pretty vitriolic reactions as well. I think that's part of what makes it interesting. The characters are flawed. They are really human.

And I'm not necessarily saying that George and Izzie are the love story of the century. People make mistakes. And perhaps this is a mistake. Perhaps it isn't. But I think it's an interesting thing to explore - that a best friend is your soul mate."

That Grey's Antomy has adventurously embraced personal flaws and mistakes is one of the traits that makes it so intriguing. How many shows, after all, have a put-upon title character who inspires so much love-her, hate-her buzz? But it's a tough act to consistently pull off.

If plot developments become too outrageous and/or annoying, it becomes much easier for us not to care. How much longer, for example, will fans put up with the George-Izzie melodrama? And more importantly, how many more Meredith and Derek (Patrick Dempsey) breakups can we take?

The cast departures also are cause for concern. Washington's complex genius Dr. Burke was a fascinating character and proved to be the perfect yin to Ms. Yang. As for Walsh's Addison Montgomery, she arrived on the scene as a bit player who you wanted to detest.

But she deepened into a strong, classy, engaging woman, a welcome respite from the intern drama queens. Both were key components.

Maybe Chyler Leigh, who joins the Seattle Grace gang as Meredith's half-sister, Lexie, will make us forget Burke and /or Addison. Maybe not.

Either way, it will be interesting to see if Greys Anatomy can recapture the magic. When the show is at its best, it delicately blends sober drama and real emotion with unpredictable twists and breezy humor.

It's a potent brew that keeps us captivated and gets us talking.

"I take really seriously what the fans say. I kind of love that so many people feel this strongly about the show," Rhimes says. "What that means to me is that they are watching it and that they care about it and that they feel as emotionally connected to the characters as I do."

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On an unrelated note, it is ironic that Isaiah Washington ended up in a show (Bionic Woman) pitted directly against Rhimes' new series, Private Practice. Washington isn't in tonight's pilot �" he will appear in five upcoming episodes �" but it will be interesting to see his return to television.

On Private Practice, Addison heads to L.A. to leave her McNightmares behind.

• The good news? Wednesday's premiere improves considerably on last May's back door pilot / preview episode.
• The bad news? It remains to be seen if this cast of all-stars (including Taye Diggs, Tim Daly, Amy Brenneman) can gel into an appealing ensemble.

Only one Grey's Anatomy character appears in this week's episode �" the chief (James Pickens Jr.), who reluctantly accepts Addison's resignation and watches her bolt Seattle. You can discuss the episode in our sister site's forum.

Steve Marsi is the Managing Editor of TV Fanatic. Follow him on Google+ or email him here.