The curious thing is I found it very hard to get the main themes for Thor and Thor2 separated in my head. Until I took a closer look and found they seem to basically sit over more or less the same chord sequence - Thor2 has more notes squeezed in but is indeed more of a development than a totally new theme. Making this particular complaint a little ironic.
I have some regret for the absence of some of the exquisite motifs from the first film in their original form, but I will say I found Thor2 one of the most enjoyable soundtracks I've heard lately with some really impressive cues.
I will also say I really don't care whether the progressions are simple or how the sounds are generated - what matters to me is the effect of the music on me as a listener. And for Thor2 that effect is certainly a stirring one.