Part 1 of the series. Part 2 of it. Part 3.
Now that I've rewatched the all the episodes that were written when Sera Gamble ran Supernatural (parts 1, 2 and 3), and we approach the point where post-Kripke years equal the number of years Kripke ran the show, what can we conclude?
Sera was given an almost impossible task that I am not jealous of her having to tackle. Like the Matrix, a definitive story arc had been told yet the audience wanted more. Not to mention being given the task to carry on the stories after someone who had demonstrated a pretty strong storytelling talent. Where and how do you follow it? In hindsight it might have been the best idea to make SPN into a mult-season anthology show, but to pull that off would have been a HUGE bet where you either win big, or lose big, so it's completely understandable why Gamble went with the safer route.
So now that we've had 2+ years of Carver, how do the Gamble 2 years compare?
Gamble loved to "play big" with the story - the arc of S6 and S7 were both world-changing (possibly destroying) arcs: Castiel is God! Leviathans will domesticate us! Carver seems to prefer smaller, more intimate, character driven arcs: the struggle between doing something good vs losing your brother, and whatever S9 was about (S10 looks to be shaping up to be a "save Dean" arc like S3).
Even more important, Gamble not only appreciated canon, but knew how to add to it and play with existing canon perfectly. Purgatory? May not have been intended by Kripke but made perfect sense with everything we'd been told. Why didn't anyone mess with it? Why the leviathans. Lucifer probably knew about it and passed the warning onto his closer subordinates while the "younger" demon (Crowley) and angel (Castiel) knew nothing about the danger. Even the addition of faeries made sense (i.e. Where were they during the Apocalypse? Probably hanging back in their own crib waiting to see whether things blow over.) It didn't always quite work (fate & the meta episodes for example) but when it failed, it was usually with smaller additions that were usually one-off episodes that could be ignored if they didn't work. Carver... does not do this. Abaddon... the Men of Letters... Lucifer's crypts... regardless of whether we fans liked whatever addition, we must be honest and admit that most of the time it's really hard (if not impossible) to fit everything together (no seriously, try figuring out how Abaddon & Azrael work and your head will explode).
Of course Gamble's run wasn't perfect. The politics of the show makers were much more overt a few times. More than once the writers showed their hands by having characters express views that logically they shouldn't. Besides, fundamentally, SPN is a world where politics is meaningless; who care what the details of the tax code are or school curriculum when Satan himself is attacking the entire world? So to try and score political points in the show comes off as very... petty and beneath the show. Sometimes they also lost control of the plot and wound up in corners they had to write themselves out of with resolutions that weren't always satisfying.
Lastly, there was also a clarity to Gamble's work that the recent years have lacked. Some might call it a lack of subtlety but at least during her run you could understand what characters' motivations and goals usually were as well as how creatures and items worked in the world. While there were still things fans could debate over, there was almost never any debate over what was happening in the show.
So all in all... I think Sera Gamble had a bit of a challenge having to follow on the heels of a very talented show creator, but looking back, nearly 3 years later, I think she did a pretty good job.