Many people say that Gregtech is a bad mod because "it makes everything difficult" or "it makes you have to <this or that or some other thing> a lot", or whatever like that. They say it takes you forever to progress in the game, and once you have progressed there isn't enough reward. Those people are actually wrong, but they don't see how they are wrong.
Using Gregtech only chances a few vanilla features, usually for balance (logs -> wood -> sticks) or fixing stupid things in the game that are the product of developers' lack of knowledge about the real world (trinitrotoluene -> TNT, gunpowder -> powderbarrel). This may appear to "make the game difficult for no reason" in the perceptions of some shallow-minded people; but it actually increases the reward you get for building machines, since your sawmill is more efficient in producing wood products (relative to the the efficiency of your bear-hands), and TNT is a product of advanced chemical engineering.
What really makes the game difficult, is the complexity of the crafting recipes, but this is entirely due to how the crafting system works. When crafting, most of the time is used to move items around in the inventory, while making the item is nearly instant. You also have to remember the exact pattern for the recipe, or use NEI to look-up the recipe. This system is a "bottleneck", as you end up spending much more time moving items into the crafting grid than the time it takes to produce the item from its components by clicking on it.
If this system were replaced by one much like that in the "mobile version' of Minecraft, wherein you get a list of stuff which you can craft instead of a 3x3 grid to place items, you could craft machines a lot faster, by first having the necessary materials and simply clicking on the list-entries for each component, until you have all of the components for the machine's recipe to appear, which is then clicked just once to produce it. However, almost every mod using the existing crafting interface would either break or become deprecated, since the "grid method" would be totally replaced by the "list method". Existing recipes could still work, but they would all be translated to a shapeless form; also, multiple similar recipes could exist, either taking the same ingredients or producing the same item from different ingredients, without the problems caused by those recipes when the existing system is used (they would simply have a different list-entry in the list, instead of overwriting whatever recipe previously used that exact pattern of ingredients)
If the game has included a list-style crafting system before Forge existed, Gregtech wouldn't be "walked on" so much, since it would be much easier to craft anything regardless of what materials it uses.
Note that "crafting something" and "gaining the resources with which to craft something later" are distinct and should not be treated as the same. Sure it is more difficult to gather resources - but these are the resources which you use to produce machines and devices which would be overpowered if it were easy to produce all of the stuff used to make them. The reward is greater if it does something which you can't do with your bear-hands, but it is not so much if it is cheap to create or you could already manually do its processes as efficient as it does them. What good is it to get to the "end of the game" in a few days, having powered jetpack suit, laser rifle, rocket gun, missile base, automatic frame quarry miner and all of that, and then realize that you don't really have anything else to do except build houses (which nobody will use) or destroy stuff for no reason? (with GregTech, you can always try to fill that Ultimate Battery or construct a more efficient ore processing factory)
Note also that "bear-hands" is intended, and not "bare-hands", because bare-hands could not rip wood logs into acceptably-formed planks and rip said planks into acceptably-formed sticks, whereas bear-hands would be somewhat more effective at such a task.
