I haven't read any of the books, but Dalgliesh the show is great. I was pleasantly surprised when I saw new episodes appear recently and watched them the instant they came out. Having said that, The Murder Room closed the season/series on uneven ground IMHO.
Part 2 starts with a body found in a way similar to another historical case from the murder room, this time in a trunk they said is very rarely opened (and was only opened this time for plot reasons). During the PM however there were flowers discovered in the victim's bra; flowers rare enough they could only come from one place on the estate. This is strange because there's no logical reason for them to be there, and could only be put there purposefully. What's worse is we weren't given a reason why the killer felt the need to do that, since the flowers and crime scene were obviously two different places.
Then there's the killer's motivation for the first murder: what was it? I watched the scene twice because I thought I missed it and there wasn't what I would call a full reveal. We were told more than once the 99 Club (or whatever) wasn't illegal or a source of profit, so why the doctor, because the killer didn't like him? Seems like important parts were either left on the editor's floor or something was lost converting from the book.
Season two ends on a somber tone with Dalgliesh watching his colleagues at the Yard hard at work, but that emotional tone doesn't really match what's happening on screen. Adam made an ultimatum to his bosses to fully prosecute the killer or he would resign, having the option to go on tour in America for his poetry. Not only did they agree to this, but they also gave him a promotion, and in turn his sergeant, so why the sad music and reflective stares? He may not be pursuing his writing career as much as he could be, but he gets to keep doing the other job he loves, and justice is being done in this case... and it looks like season 3 has already been approved. Everybody wins here, but the tone makes you think otherwise. Cheers!
Update: thank you for the reminder MsMisto. Would've been nice if the killer referred to the lease issue in any way; such as the actions were to protect jobs or property rights... By all appearances the killer was unhappy and unliked by almost everyone, so I still question the motivation because it was neither selfless nor selfish. It felt more like the actions of a hired killer, which isn't the case at all. As you said, the killer was not a real factor in the script.