First of all a show has to respect both its characters and its audience, which automatically filters out a bunch of fanservicy trash. Beyond that:
* An interesting setting
Ex.:
Log Horizon - takes actual MMO gameplay mechanics and works them into cohesive world building the characters have to try and build a sustainable society in.
* Story goes meta or dabbles with the concept or creativity in some way, and how that clashes with reality
Ex.:
Re:Creators - characters from several kinds of fiction manifest in the real world and clash with its more nuanced realities and each other's tones, and confront their creators about the realities inflicted on them;
Abenobashi - a character about to see life as he knows it fall apart through changes in his neighborhood find himself transported to all sort of worlds based on things he likes, gradually discovering that he's unconsciously causing that, and that something related has been heavily involved in his family's history.
* A concept that's incredibly silly but executed in a fun way
Ex:
Girls und Panzer - competing in WW2-era tanks is a lady-like sport practiced between schools for girls which appear to be the linchpin of cities build on airplane carriers, and the whole thing is steeped in a passion for the history and engineering of the WW2 era, which would make for a weird combination, but then
the combat coreography is insane in the best possible way
JoJo's Bizarre Adventure: Battle Tendency - people with sun-based martial arts fight naked men that eat vampires, but the protagonist is a joy to see in action.
* Something slice-of-life that touches on some topic of interest
Ex.:
Genshiken - shenanigans of a college club that revolves around geeky hobbies; the focus of the club served as the "bait", but the character dynamics develop in interesting ways
Silver Spoon - life in an agriculture-focused school, with more than a few interesting lessons and fun moments along the way