I love Las Vegas, it was a great show that unfortunately ended at season 5.
This season is fun, pure, unabashed fun. While other reviewers may harp at the comical death of Lara Flynn Boyle's charter, for me it worked. The character could not have continued in the show without a full out, Spartacus style, rebellion on her hands, which, while interesting, would not have fit the shows' style.
This season gives us more depth on our main cast, as well as the expected celeb. guests/musical acts. Heck, I'm by no means a country music fan, but it works. Expect to see some familiar guest stars, and some new ones, who may, or may not (it has been a while since this show was on tv) return.
As to comments about the departure of the Nessa character, while no explicit details are given, she is mentioned several times, and there is character conflict about her disappearance, throughout the entire season. To me, this is more then most shows give the exit of a cast member.
Finally...don't let your kids watch this. While every season bears the 'uncut and uncensored' descriptor, this season actually lives up to the name. There are several scenes spanning a few episodes, that certainly did not make it on network TV. You may get an eye full the first time we enter the Bella Petto ('European' style pool area), and the Vegas off-strip, strip clubs.
All in all, a fun, goofy, well written, directed and acted season, with a decent cliff-hanger ending.