So, let's check how they grounded the GL character. Ryan Renolds, check. Few actors bring grounding to a performance like he does and still be so likeable and interesting. His ability to show a wide range of human emotions really helped. He just appears genuine, all the time. It works in every movie I've seen him in.
Cool girlfriend. Cool best friend. Check. Both dynamics worked well and created an empathy wedge for a vast portion of the audience to connect. The writers seemed to know it would be difficult. Aliens. Will. Fear. Thought magic. So many of these factors dehumanize the movie. My wife said it best 2/3 into the movie when she declared, "That was all plot setup." They took their time, and by the end, I cared about all of it, even the weird alien lantern cult.
The villain was a creature of fear who seemed to use others' fears to consume their souls. He grew in size every time and became large enough to engulf entire cities like a giant space octopus. I had flash
backs to Fantastic 4 and Galactus, where I didn't really care about the planet eating space cloud coming to Earth. However, when Parallax was growing, and I knew his condition and his power (because the movie explained it to me) the threat felt real and my suspension of disbelief was supported. Then when I realized he was going to go building by building over the entire Earth and eat everybody, then the movie really had it's hooks in me.And when Hal said, "At least let me try to defend Earth," I became a fan. He wasn't going to thwart their plans. He was asking to have a chance to save Earth or die trying. Then they could put their plan into motion. No buffing the system that was obviously bigger than him. No going against their wishes. Just a plea for a chance. Thank you for that, Hollywood.
This type of writing made me like the movie.
PS. The following thought didn't flow in my rant, so I'll drop it at the end here. Superhero movies have a problem that's becoming more and more obvious. In order to tell the story properly, they need to show violence. Yet the PG-13 line comes quickly. Crossing that line means a smaller viewer demographic. Yet not showing the violence tames the movie in a boring way. I cannot find what GL was rated upon release.
I enjoyed some of the violence they showed in GL, for the mere fact that if I were a sniveling villain who just acquired ultimate power, that's exactly how I'd behave. Showing the violence brings much greater risk to the heroes in viewer minds, if we are made to believe the movie doesn't care about such lines, then the risk is more palpable to us.
Let me illustrate with a stream of consciousness reenactment: That man just killed that woman and his own father in a terrible manner. I didn't even really care about those people. When the climax of the movie comes, in order to outdo itself, the movie is going to throw something even more horrible my way.
I wasn't disappointed when it didn't happen, because the feeling was there all the way to the end. That emotional ride is what I enjoy the most in a movie (besides tight plot points, a sweeping plot concept, and witty dialogue). It wasn't the greatest movie and it wasn't supposed to be, but it did well for me. They creatively handled what I thought were insurmountable plot obstacles by crossing a few lines to make it feel more dangerous.

