I could go on and on about how I use the mods, and early-game vs. late-game and all that...but it basically boils down to this: When I play, my base is either IC2/Gregtech, or everything else. There's always a bit of room for crossover depending on what I'm trying to accomplish, but 90% of the time when I walk around my base, my ore-processing and my power production and my materials management...it's gonna be IC2 or everything else.
That being said, IC2 and Gregtech 100% have a place in my heart. In fact, it's more than that. IC2/GregTech Minecraft feels like real minecraft. Like, how it's supposed to be played. I've outlined before how the crafting recipes of a lot of mods bother me. Throw some smoothstone and some glass and some redstone together and...COMPUTER? Part of me really likes the extended production line of building parts of parts and bits and pieces - it keeps me in the narrative of "here's a dude with nothing but his wits and things he's built from raw resources." I am dubious of my own ability to do something like build a generator or an ore crusher or a solar panel, and so seeing my steve run around building knick-knacks that will eventually fit together to become a windmill feels more real to me. But also, I totally get that some folks prefer the implied/obfuscated methodology of Iron+sticks=pick. No need to build a freakin machine to turn the ingots into plates of iron and a separate freakin machine to lathe the wood into rods and whatnot. Explicitly spelling out the tedium/grind of building a machine by requiring a dozen extra steps isn't everyone's cup of tea. Sometimes, it's not mine either. I totally get it.
But in the end, I'd be sad if IC2 stopped being a thing or option or mod in the pack. I feel like especially for late-game stuff with my crazy AE system and my fusion reactors and my solar panels, having banks of machines building parts for other machines feels right. But also, these days I've got work and real-life and even other games that I'm into, and as a result, the hours and hours of added gameplay that IC2/gregtech offer no longer seems like a fun means-to-its-own-end. That's not to say that I don't appreciate what the mod devs are doing...it's a bit like when I'm trying to pick out a new book to read. I can sit down and read my way through my favorite book of all time - The Count of Monte Cristo - it's long and has a few boring parts and the language is a bit goofy in spots and it'll take me forever and a half to read even for the tenth time but damn is it satisfying. Alternatively, I can pick up something shorter, easier, and perhaps something that I haven't experienced before. Either way, I'm gonna enjoy a book. It's just a question of how much time and patience I've got, and whether I'm gonna have the stamina to see it through to the end of am I gonna cheap out halfway though and build a bunch of mekanism machines because I just wanna get to endgame already for this run.
That was longer and more rambly than anticipated, but I hope that at the very least, I could kind of give a tiny bit of insight into why I love these mods.