To me there are three kinds of 3D movies:
You have the 3D presented by Avatar, where it was actually filmed in 3D. In my opinion, this is freaking awesome.
Then you have the 3D presented by Alice in Wonderland, movies that were filmed in 2D but at least took into account that there was going to be a 3D release. Not as good as Avatar's, but still cool.
And finally you have the 3D presented by Clash of the Titans, movies that were filmed in 2D, meant to be released in 2D, but the studio decided to just tack it on because 3D is making big money. This 3D sucks ass, especially if it's tacked on at the last freaking minute.
So in conclusion, if you're going to release a 3D movie, don't half-ass it, go all out or at least make sure that you take into account that the studio wants to release it in 3D so it won't look awful.