I do love Gregtech. I think I would 'finish' minecraft way tooo quickly if not for the grind of GT, and really lose that sense of accomplishment.
And while I won't play modded MC without GT anytime soon in the near future, I do wish some things were more suited for single player only. In particular machine processing times. God I wish there was a config for this. Bump up the energy draw if you must, but I hate waiting for simple things to finish processing. Even with a complete 150 eu/t draining AE system I still have to wait....wait....wait... for even relatively common recipes (any circuit, whether that be advanced or energy orb or w.e) to be crafted. I also hate the lack of documentation, when resources weren't 'unlimited' I had dished out alot of iron for a Large Steel Turbine, only to find out you pretty much need his tesseracts in order to supply enough steam. So a simple steam turbine ends up needing several iridium plates? Well crap.