I really love the high school seasons dearly, but starting with Season 5, the show really picked up-- the adult storylines for the characters became deeper, more complex, and in some ways more emotional. This is a great season as we finally see dreams come true, but a sad one as some good-byes are in order (Chad Michael Murray and Hilarie Burton, Lucas and Peyton, have since left the show).
This season is a great one for all the characters. Lucas and Peyton get engaged and end up struggling with Peyton's difficult pregnancy. Brooke becomes a foster mom to a girl much like herself as a teenager, and finds herself falling for one of Peyton's exes, a movie producer named Julian. Nathan and Haley continue to parent their adorable son Jamie, as Haley ponders returning to her singing career and Nathan tries to build a comeback in order to have one last shot at his NBA dreams.
This season is probably one of the most emotional ones I can think of since Season 3. The third episode, "Get Cape. Wear Cape. Fly.", is particularly moving, and the subject of Keith's death is revisited in a few episodes. And of course it's sad to see Lucas and Peyton go after six seasons' worth of the show's five-man band. The show has soldiered on without them and it's still pretty good, but in some ways, it's missing something.
I really recommend the season for fans of the show. For newcomers, I'd recommend either starting at the way beginning in Season 1, or at the very least starting at Season 5, when the show reboots with a four-year jump into the future (this season is a direct followup to that one). It's a well-done, fun, and sometimes emotional show, and definitely not a disappointment. You'll like spending time in Tree Hill.