If Green Lantern can't be a successful movie, then it can't - but this movie was observant and faithful to the spirit and most of the details of the Green Lantern comic.
I think the key is that it's faithful to the spirit of the simple, cornball original
comics. Those are the ones I grew up on, and so I never have a problem when a movie like this (or Superman or Spidey or the Rocketeer) goes for the same kind of simple, cheesy tone.
Of course today's comics are MUCH more intricate and complex, and I get the impression that's what most people expect from the movies as well.