Now that the season is over, looking back on it the things that most stand out was that this really was the season of the crossover - we had The Simpsons meeting characters from Futurama, Rick & Morty, and Family Guy (not a Simpsons season 26 episode, but it did air during this season). We also had a couple internal crossovers with THOH XXV's The Others parody featuring the Ullman era family and a full Kang and Kodos episode. Another major element to this season was questionable continuity, as both Simpsorama and The Man Who Came to be Dinner did some truly outlandish things with no real framing device to explain if it was canon or not. I really wasn't bothered by this, as we've seen THOH episodes and video games (The Simpsons Game, Hit & Run) that get really outlandish without any explanation.
Standouts: "Treehouse of Horror XXV", "Simpsorama", "Covercraft", "I Won't Be Home for Christmas", "My Fare Lady"
Good: "The Wreck of the Relationship", "Super Franchise Me", "Blazed and Confused", "The Man Who Came to Be Dinner" (controversial episode, but I liked it), "Bart's New Friend", "Walking Big & Tall", "The Princess Guide", "Sky Police", "Waiting for Duffman", "Bull-E", "Mathlete's Feat"
Middle of the road: "Opposites A-Frack", "Peeping Mom", "The Kids Are All Fight", "Let's Go Fly a Coot"
The disappointments: "Clown in the Dumps", "The Musk Who Fell to Earth" (though I liked that it set up later episodes and provided a season arc)
I enjoyed season 26. There were only two episodes I disliked, several good episodes, only a few middle of the road ones. My only complaint really is that the standouts were for their high concepts. "Covercraft" and "My Fare Lady" were my two favorite "traditional" episodes. I'd give the season a solid 4/5 because there really were a lot of episodes I enjoyed and ended up rewatching.