From what I've seen of Reynold's in interviews and his SNL appearance he seems like a down to earth guy, doesn't take the Hollywood fame too seriously so yeah he seems likeable.
And he seems like a practical joker on set, supposedly Wesley Snipes couldn't stand him when doing Blade 3 but who's to believe in this case and he was funny as Deadpool in Wolverine.
Maybe his charm can make Green Lantern a sleeper hit like Iron Man only thing is the character of Tony Stark is a carefree playboy so RDJ playing him as a jerk is normal, I don't think Hal Jordan can be played like that but we'll see next summer.