Doing a "sorta" rewatch. Something I observed....
I only wanted to watch seasons 5 and 6 since I've rewatched the entire series numerous times. It seems that each time I watch season 5, the better it gets. The first time I watched it, as it aired in real time on ABC in 2009, I wasn't blown away by it at all except for "The Incident" parts one and two. "Follow the Leader" was a good episode as well that lead into "The Incident" very nicely.
It seems season 5 has been highly regarded by a lot of viewers over the years, and I can finally see why over numerous rewatches (and my advancing age. I'm 42 now versus 28 when it initially aired). Some very intricate storylines that interweave throughout the proceeding seasons and even sets up season 6 nicely. Say what you will, even if you didn't like the overall story, but the writer's are pretty damn smart in the big scheme of things.
Season 4 on the other hand, I still could do with out.