According to MSNBC, it's the tried-and-true medical drama setup (good-looking doctors, talented guest stars, compelling medical scenarios) combined with a top-notch cast of characters with real depth and no shortage of sexual tension. In other words, Grey's Anatomy.

Assembling a group of talented actors and actresses without a bona fide star that distracts from the other cast members is a challenge, but Grey's Anatomy succeeded. Whether it's The Girl from Old School (Ellen Pompeo), That '80s Teen Idol Guy (Patrick Dempsey), or the Girl from Sideways (Sandra Oh), the cast members are recognizable, but not big enough to detract from the show as a whole.Throw in terrific but unappreciated performers such as Isaiah Washington, T.R. Knight and Katherine Heigl, and you have a group where any plot or combination can carry the show.

The characters geared towards establishing a rapport with the audience, and giving every viewer someone they relate to. While Meredith (Pompeo) is the central figure, George O’Malley (Knight) is the conscience, an "everyman" and lovable loser destined to be an audience favorite. Drs. Bailey (Chandra Wilson) and Webber (James Pickens, Jr.) are endearing, but no-nonsense bosses.

The list goes on and on. The show's relationships are much the same, with enough humor and inappropriateness to seem real. While the show benefitted early on from following Desperate Housewives on Sunday nights, it's become a bona fide hit in its own right. With creator and producer Shonda Rhimes leading the way, there's great writing, filming and pacing. While there's the occasional medical drama -- read: Code Black -- the show is rarely predicated upon intense ER-style action scenes.

Therein lies the beauty of our favorite program. Grey's Anatomy is primarily character-driven. Because of this focus, viewers each have favorite characters and storylines they want to see more of. Even as an ensemble cast limits each character's screen time, they're all well-rounded.

Well, most of them anyway. Macho loose-cannon Alex Karev (Justin Chambers) is one-sided, but still erratic enough to keep things interesting. Alex's love interest, Izzie (Heigl) has a perplexing trailer park back story, but she's just rough enough around the edges to pull it off. It's a group that turns out great episodes week in and week out, but some critics think it will be tricky for the show to sustain its momentum, for a number of reasons.

• The complex relationships and romantic interplay between the characters makes for good TV, but it's a fine line. Keeping ideas fresh and making them compelling (rather than ridiculous) is an uphill battle over time.

• So many strong characters make good TV. They also make it hard to keep actors and viewers happy. There are episodes when the focus is on Dr. Derek "McDreamy" Shepherd (Dempsey), then he pretty much drops off the map for weeks at a time. Some actors may grow unhappy with their roles and leave.

Whether that happens remains to be seen. So far, however, all is well in the Seattle Grace Universe. The show's talent continues to produce, and the recurring story lines keep legions of fans coming back. We hope to do so for years to come.

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