I started playing today and the way the cubes load up the 2D images appears to have changed. I’m using Chrome on OS X. Yesterday it was very fast and you could start flipping through the slices immediately. Today each slice loads up as a very lo-res image, before each quarter loads the final image (one section at a time). It’s quite slow compared to before. I’m finding I have to load it and leave it for a minute or two before working on it. Just an fyi in case this in not the desired behaviour.
Image loading has changed, but about 3-4 days ago, and hopefully for the better. The low res image is prefetched before the high res images (to make scrolling more fluid), but when you stop at a slice it should immediately try to load the high res image.
It’s possible things were slow for you because of load on our servers, or due to network problems. Please let me know if the issue persists over the next day or two.
Seems like this is still happening for me, but if it’s the behaviour you’re expecting then no worries. I don’t find it as fast to load as it was previously, but if it is better for the majority of users then I won’t complain. 
I’ll definitely look into it then. Data loading is never a solved problem, it seems! I’ll let you know when I’ve revisited this, it will probably be about a week from now.
It loads much better for me than last time I was here; now the blue never lags being the rest of the picture. Thanks I am also using Chrome.