I'll definitely second the preference for a more involved power system. AC/DC, large multiblock transformers, and importantly, a reason to use them. The present trend has been along the lines of 'there's a bad cable and a good cable, and we're going to limit your use of the good cable by making it more expensive', which always seemed unimaginative to me. I'd rather have the limiting factor be the hulking transformer station you need to convert down to a usable amperage!
I'd also like more focus on interesting generation options. The RP and BTW wind turbine / wind mill are good examples, as is the BTW water mill. Steam boilers and Atomic Science fission reactors are as well, I suppose GregTech and Atomic Science fusion reactors, too. In essence, if something is going to a significant amount of power, I'd much rather have it be a cool spinning thing which makes some sort of 'real' sense, rather than a single block hidden in a wall somewhere.
Actually, I think my overall theme here is that I wouldn't mind if power systems took more space at the generation and processing points, and less at transfers (redpower-like cables). In a way my perfect power system already exists, it's just spread out over 5-6 mods which don't like each other very much, and / or have absurd conversion rates. Heck, the other night I was toying with a Mekanism hydrogen generator, and found that just by changing the output type it was either very good or downright power negative. Silliness.
Also, I want multiblock structures which look nice, but aren't necessarily stupidly expensive to make. Because I quite like having a reason to make an actual 'power room'.