I wouldn't have minded the movie being set in the '80s, so there's one...
My biggest problem with the exo-skeletons is how much they look like the Halo character. It seems like they were designed just to appeal to that audience. I'm not sure that I mind so much otherwise.
Personally, I think if they went with the original costuming, it would come off like the Brady Bunch Movie. I'm happy that they've updated things.
I've heard lots of people complain about the exo-skeletons. (Even when I tell them I'm not a Joe fan. All part of the job, I guess...)
What I've countered with is this:
When the GI Joe cartoons aired in the 1980's, the Joes used tech that was pretty far advanced of what was available at the time. It's now 25 years later, and a good chunk of that tech is now either available, or within sight. They needed to advance the Joes to match the advances in the real world.
Unless they were going to set the movie during the 80's, but I doubt anyone wants to see that.