MOS to me was a misstep. Setting it in the real world was infuriating! It was trying too much to emulate the success of the Dark Knight trilogy. Instead of expanding a universe that was quasi-reality, it tried to set it up in our reality "to give more emphasis to Superman". Now instead of breaking open a universe that is open to anything, it limited that option. So instead of having mutants, semi-advanced technologies, aliens (more than Kryptonians!), magic, we get our plain old boring reality. So moving forward, how do you explain a Martian, an Atlantean, and Amazon, a universal police force, and a man who can run at impossible speeds? They are going to have a radical shift in reality.
Considering they could have started off in a reality that is open to other fantastical elements (think Big Belly Burger, instead of I Hop) they painted themselves in to a corner. So unless you read tomorrow that they've discovered life on Mars, you won't get fantastical antagonists to go up against the heroes.
One more thing lacking in MOS, no levity! The sense of wonder of his powers wasn't played with enough. It was all deathly serious like TDKT! That was what Avengers had that was painfully lacking in MOS.
In regards to the Flash, if it does go to series, it shouldn't follow the template of Arrow and go almost 180 degrees in the opposite direction! Barry should be more uplifting, with a source of awe and wonder as he discovers what he can do. Not like Arrow with its sense of foreboding and burden that Oliver carries. It will fail if it copies the same formula. I mean who would even want to see a show with the same tone?
That's just my two cents.