I'll go out on a limb and say that I thought the casting of Ryan Reynolds as Hal Jordan/Green Lantern was brilliant. Unfortunately, he was saddled with a TERRIBLE movie that seriously lacked the kind of vision necessary to pull off a Green Lantern film.
It's true that the Green Lantern is a really weird superhero concept when you get down to it. Intergalactic space cops with fantastical rings that make their thoughts take form as solid green light, limited only by their imagination and willpower, and resulting in crazy-ass imagery like someone willing a green racecar into being just to catch someone, or willing a sword or machinegun or giant fist into existence to hit an enemy. That's....pretty wacky stuff.
But the thing is, Jack Kirby's version of Thor is no less wacky, what with the TOTALLY outlandish costumes, fantastical Asgardian setting, thees and thous in speech patterns, etc. And yet, even the first kinda ho-hum Thor film was pretty good, or at least was good enough that you never looked at things and thought "My god, this is just laughable!" Sadly, that was not the case with Reynolds' Green Lantern.
And the thing is, as Hal Jordan, at least the version that I'm most familiar with (starting with the Geoff Johns' era relaunch in the early 2000s), is a character almost perfectly made for him. He's cocky, brash, kind of a jerk, but also has some deep-seated pain and anguish in his life, much of which he's just trying to push past. PARTS of the film tried to show that, but the execution of the film as a whole was just lacking. And the final bad guy being a big cloud of evil was just idiotic (exactly as it was in the Fantastic Four film with Galactus being a giant world-devouring tornado).
Anyway, great casting, lousy film.
Reynolds as Deadpool was PERFECT, too. I just watched that this past weekend, and I have to say it is one of the most entertaining films I've seen in 2016. I liked it better than Civil War, actually.