IC2-Experimental kinda killed IC2, for me. Why? As was mentioned before, the "punishment as difficulty" was one of the main contributors. Let me just say that I don't really mind needing plates for some things, and the forge hammer is a reasonable way to acquire them. Hell, once PowerCraft comes back for 1.6+ (something on which I and others are working as we speak), it'll be a good thing for packs on which I play that contain both PowerCraft and IC2, since I'll be able to make those cool-looking iron frame blocks again, as the iron furnace needs iron plates instead of ingots. However, the energy net took a bit of a dive off the deep end and became even more brutal than usual, since now, even a single 1 EU/t solar panel can mean the difference between wires melting and/or machines blowing straight to hell. The latter, of course, has always bugged me about IC2.
Then, there's also the fact that other mods have come on the scene that do much of what IC2 does, only in a way that I, personally, find more enjoyable. Mekanism has simpler power transfer and better, more intuitive ore processing, along with the best automated mining of any mod I've ever encountered. Thermal Expansion's also a top contender for simpler, less intense power generation and transfer. Hell, even BuildCraft has better, more forgiving power than IC2. Its not the wires melting that I mind; wire is, for the most part, pretty cheap and easy to come by, especially later on in the game. I just don't like having craters because I accidentally got a wire crossed or misplaced something. You could have the machines break without having them explode. This also leads into the wrenching mechanics which are, have been, and seem as though they will always be supremely annoying. I shouldn't be punished for wanting to rearrange a few machines. Mekanism doesn't punish you that way. MineFactory Reloaded doesn't punish that way. Thermal Expansion doesn't do it, RedPower doesn't do it, the list goes on. That's something that seems to be completely unique to IC2, and that's not a good thing...for IC2.
I realize that the current build is labeled as "experimental," and a lot of this may likely change. That, however, doesn't change the fact that, as it is right now, IC2 is a supremely annoying mod that's being outstripped by its competition in almost every field.