Jotenheimen is amazing, as you say, its up on a plateau, so you go up and then when you think you've got to the top, the mountains spring up and they are a delight. Fair takes your breathe away.
The key difference for Galdhopiggen is that it doesn't have a tourist route to follow, so although its technically not difficult, the traffic flow is much lower, and there is a large cafe on top, which is needed to dry your clothes and warm up when you get there (if its been raining all the way up
). We went with a guide and parts of it we were roped up (although this seemed to be a bit over the top as the crevasses were quite thin and easy to step over). One guy slide on a bit of glacier when we weren't roped up, but we caught him.
I would definitely suggest going in a group if you are unsure. The going is very rocky, I mean, very rocky.
Its a long day so take a packed lunch
The cafe to dry your clothes in
This is the bit where we nearly lost someone, its an easy bit so we weren't roped up, but he lost his footing and started sliding, luckily I had my microspikes on and was able to reach him in time.
This is where you get roped up
Some of the crevasses
Did I meantion it was very rocky?