This is one of the better seasons of the 'late period' of ER (past season 8/9), with truly interesting plotlines. Greg Pratt, Ray Barnett and Neela Rasgotra get the most character development this year, which is good as this changes things around a little, as most character development tended to be on Luka and Abby for the past couple of seasons. Both do get major screentime though, with their plotline, which is great as Maura Tierney and Goran Visnjic are excellent actors.
The stronger episodes for me were Blame It on the Rain, Dream House, the usual stunt episode Two Ships and Darfur. The final 3 episodes, There Are No Angels Here, The Gallant Hero and the Tragic Victor, and 21 Guns may be the strongest close to a season ever, all are highly dramatic and a pleasure to watch. Special mention must go to the episode Body & Soul, with James Woods as Dr. Nate Lennox, for a very well crafted and emotional episode, possibly the best of the season.
In conclusion this is definitely a good season, but it is worth buying earlier seasons first in order to watch the characters develop and mature. A good purchase!