I'll admit that the movie did have some obvious mistakes that were pretty frustrating to watch, but it wasn't completely terrible.
I think that its main downfall was that it borrowed the main plot from the books and then attempted to simplify it to make it easier to understand. But in the process, they kind of skipped past a few crucial details accidentally.
Not all of your points are entirely valid though. The movie ended with a "To be continued..." because there were four books in the series. The same goes for The Hunger Games and Divergent. If they just made one movie for three or more books every time, majority of the movies we know today would take hours and hours to watch. Just think of Harry Potter, Twilight, The Chronicles of Narnia, etc.
Some of your speculations were absolutely spot on though. It makes no sense whatsoever that the Glade was so grassy and green, even though the earth was supposedly scorched and hot as hell.
It makes more sense in the books, because (it explains that the maze was actually underground in a temperature-controlled room, and the sky is just a ceiling that W.I.C.K.E.D used to trick the Gladers into thinking that they were outside. But the movie completely messed that up.
In the books, the "sky" was always a clear blue, and the weather never changed-no rain, no clouds, nothing. Because it was a projection that W.I.C.K.E.D created.)
Also, in the movie the boys make no move on Teresa. But it's only logical that they would, right? A crowd full of hormonal teenage boys who haven't touched a woman in three years, yet alone even seen one and yet they basically look at her as if it's a common thing to have girls show up out of the blue. Seriously?
In the books, (they all call dibs on Teresa immediately.)
My advice is, don’t waste your time on the movie and read the books if you haven't already. They are 100% mind-blowing and keep you guessing until the very end. There’s The Maze Runner, The Scorch Trials, The Death Cure and The Kill Order.