I wouldn't recommend Real 3D, but that's not saying it was 'bad'. For me, R. 3D only got me spending more, and I'm not sure whether this was exclusive to R. 3D or just the way it was filmed - but some fight scenes were hard to follow, and there was a slight blur at times.
As I said - that might not have been the R. 3D's fault, but I'm not ruling that out.
I'd definitely suggest IMAX 3D, though - just because of the fact that it's IMAX. To witness Thor on that grand a scale is truly breath-taking.
Nevertheless, 2D doesn't disappoint - and you'll feel, more or less, the same feeling of hype and excitement after your viewing.