I'm going to start off and say that I like GregTech. I use it a lot now that it's grown on me. I like the added challenge, because without it I hit end game way too quickly. I'm fine if he edits IC2 and Advanced Machines, Advanced Solar Panels, whatever. That's IC2. It's in his department, and it was added to Ultimate and Mindcrack for a reason. Here's my issue, it's when he starts changing other mods. Quarries requiring IC2 Diamond Drill is ridiculous, especially with GT installed Diamond Drills are quite a bit more expensive. Here is a list of non-IC2 things he either nerfs or edits:
Duplicated Dragon Eggs, this sucks for servers if everyone wants an egg.
Enchantment Table Disable, this is not true by default, but is an addition that shouldn't have even been thought of.
Forestry Bronze, Forestry bronze can be crafted I think with the ratio dust:bronze 4:4, he makes it so that it is 4:2, which is ridiculous as it requires 4 dust to make bronze.
RedPower Block Breakers, I don't even understand why this is in the Config. What is so OP about a damn block breaker? What if CC isn't in the pack, you can't make block breaker farms. It is false by default, but still possible to nerf.
TE Recipe Hack, I don't know what this is, but it still interferes with Thermal Expansion, which is not IC2 related in anyway, and the difference has cause many flame wars.
(all of the above are considered features. No, those are not features, those are possible nerfs.)
I am okay with Greg using other mods items to make his mods items. That is fine with me, and is often cheaper and UP.
BC Quarry, requires a Diamond Drill instead of a Diamond Pickaxe. Ridiculous.
Now, I know this is IC2, but I wouldn't have an issue if the Quarry recipe wasn't stupid: Diamond Drill, requires steel, titanium, and an advanced circuit.