There has been a pattern in the writing of NCIS that has always been fascinating. Ever since "Bete Noire" in Season 1, this series has always used it's season finale to essentially set up the next season's finale. "Bete Noire" introduced Ari Haswari. In the finale to Season 1, Jethro Gibbs shot Ari to cover Haswari's double agent status--though Gibbs would have preferred to kill Ari. Because Ari wasn't killed at the end of Season 1, he was able to murder Kate Todd at the end of Season 2. Because Ari shot Kate at the end of Season 2--and more importantly, WHY he chose to murder her--we were able to get the backstory of Gibbs revealed, the tragedy surrounding his first wife and daughter, which culminated with Jethro leaving the MTAC at the end of Season 3. Because of Gibbs' "retirement", NCIS Director Jenny Shepard was able to initiate her off-the-books operation against Rene Benoit, using Tony DiNozzo to romance La Grenouille's daughter Jeanne.
So as we get into Season 5, we have the culmination of Shepard's attempt to avenge her father's death by killing Benoit, though she crosses both the CIA and the FBI in the attempt. "Bury Your Dead"--especially its final scene--sets the tone for the season. Though the show has its usual action, interplay between its characters, and bawdiness that has made the show such a wonderful view, there also seems a certain weight to the season. The regular viewer knows the story with The Frog isn't over, moreover there has to be a deeper reason why Shepard seemed willing to pursue Benoit without government sanction. It is the playing out of this season that, again while the season has its usual fun, seems to give the season a somewhat sad tone.
Still, the performances are at their usual high standards. Mark Harmon's Gibbs is his usual self, though we are once again shown more of Jethro's past and his genuine heart. While Michael Weatherly's Tony DiNozzo is his usual obnoxious self, the aftermath of the La Grenouille affair leaves our boy shaken, both because of his feelings for Jeanne and being used by Shepard. Tony's conscience comes in the form of Ziva David; who, while enjoying her usual verbal sparring with DiNozzo, also makes Tony own up to his feelings about what happened and what it may have done to Jeanne. Cote De Pablo's Ziva, with her hair straightened and deemphasizing her widow's peak, becomes a more Americanized woman (and the shots of Cote bending over ain't too bad, either). We didn't have an episode that featured Sean Murray's Tim McGee a season after The Probie's year with his nom de plume (Thom E. Gemcity), but Pauley Perrette's wonderful Abby Sciutto gets her usual fun, especially in "Dog Tags". David McCallum's Ducky Mallard is most representative of the tone of the season, because he becomes privy to the secret that Jenny hides through the season.
This leads to Lauren Holly, and the end of the Jenny Shepard storyline. Shepard seems calmer this season, especially after the disappearance of The Frog (Even propositioning Gibbs in "Lost And Found"), but we figure something had to have been motivating Jenny attempting something that would compromise the agency. That something plays out through the season, and is revealed in "Judgement Day", the two-part season finale, which of course sets the table for Season 6.
The high points of this season are "Ex-File", in which a part of Jethro's past becomes a part of an investigation (Plus, we get a visit from Susana Thompson's Hollis Mann--this episode is capped by a wonderfully sad sequence at the end), "Internal Affairs" (The body of La Grenouille resurfaces, and we meet Rocky Carroll's Leon Vance--Carroll draws greatly from Daniel Benzali's character in "The Agency" from earlier this decade), "About Face" (Where Brian Dietzen's Jimmy Palmer is featured, and reveals a slight obsession with footwear), "Judgement Day" (Which brings Gibbs and Shepard's long-ago Paris operation--the one where they also became lovers--to a full circle, as well as Jethro coming to a sad conclusion about the murder of The Frog), and the simply magnificent "Requiem", in which Gibbs, while aiding the now-grown best friend of his late daughter, is finally able to put to rest the loss of Shannon and Kelly.
Performances of note are Joe Spano--we don't see as much of Tobias Fornell as we usually do during a season. Susana Thompson, whose character retired from the Army when she realized Jethro hadn't recovered from losing his wife and daughter (Why do I suspect that Holly will appear again--in Hawaii, living on the grounds of a novelist, and driving a Ferrari?). Susan Kelichi Watson's Nikki Jardine, the NCIS Intelligence Analyst who happens to be a germophobe (Leading to many moments where the team exploits Jardine's phobia for their humor), and Muse Watson returning as Mike Franks in the season finale, with his usual cowboy demeanor. But Cameron Goodman's performance in "Requiem"--as Maddie Tyler, Kelly Gibbs' best friend as a child--gives the episode the impetus that sets Jethro toward finally making his peace with losing Shannon and Kelly.
NCIS has always been a fun show, with an ability to wrench at the heart in unexpected moments. This is a season that has an underlying tone of sadness and impending tragedy, and it gives the season some unusual depth.

I've enjoyed all of the seasons of NCIS and am especially happy to get the 5th season at a discount.

The fifth series has all the drama, suspense, action and sex appeal of the previous seasons. The characters and the show itself appears to be improving with age. Gibbs is still the man that every woman would love to take home, DiNozo is the naughty big brother, Probie is the nice guy next door and Zeva well she is a sexy kiilling machine that most men would die for. These characters are loyally supported by Ducky and Abby who are both quirky to say the least! It's a great show and a great way to relax and waste a few hours.