IC2 is such a small mod, or used to be, that it really needed a large mod like GregTech to supplement it. Lately, with IC2 expanding and changing so much, with a lot of GregTech influence, that it almost seems like GregTech is about to become IC2 standard. I liked GregTech a lot more in 1.4.7 where it was a lot less intrusive. Changing some of the basics of IC2 is ok, but changing the basics of the vanilla game is a bit too far. If i wanted something that wasn't Vanilla+Mods, then odds are i'd play a different game all together. IC2 needs an add-on like gregtech. Forestry, Buildcraft, Thaumcraft, Tinkers' Construct, and IC2 all have really good add-ons, but none of them completely rewrite the way you have to play the mod let alone the Vanilla game.
I played the Unhinged modpack and was quite entertained by it, mean while calling Greg an asshole and laughing half the time, but entertained none the less. I didn't stop playing it until i hit the wait for Iridium stage of Gregtech. Shortly after, 1.6 packs started rolling out on various launchers.
Actually all of us LOVE when mods change vanilla. Because that is what every mod does. People often say
"changing vanilla went too far" but really it's that the changes made things harder. No one cares that mods allow people to change the basic vanilla mechanic of 1 ore = 1 ingot. Right? Or a mod like Better Enchanting that changes the vanilla rules on how enchanting works. These mods don't overwrite the original recipe or mechanic, but nerfs only work if you eliminate the original option. It doesn't matter that better enchanting leaves you the option to enchant things randomly, no one will use it when the can choose sharpness with just a piece of paper and 1 flint.
Once we got used to the changes, my group likes them. It extends the early game and really makes achieving the machines to make plates or cut logs feel very satisfying.