My group of Server Mates played Resurrection when it first came out. It was a very different experience from the 1.6.4 Monster pack we came out of, and most of our group was unprepared for the change. Due to that, my experience with the pack ended earlier than I would have liked.
All in all, I found the pack well balanced. From what I understand, the pack ceased to be updated after GregTech 5 was abandoned with the promise of GT6 on the horizon. Since GT6 has yet to launch, the Resurrection pack is in stasis, with little hope of revival. Nothing says you can't play it as is, or even update all the mods you can manually and hope for the best.
The TPPI2 pack is the framework for a pack based around the upcoming GT6, and it is playable now, even without it. When GT6 is ready, it will be added into the mix, or so I've been told. If you were so inclined, you could either start now or wait for the big add, although the timeframe is uncertain.
Another way to go would be Infinity 2's Hard/Expert Mode. It's not GT, but it is highly tweaked to provide a more progressive (and some say grindy, but that gets said of GT, too) experience. Many of the mods are similar to Resurrection, but Infinity carries a number of mods not included, and the progression between the two packs is likely quite different.
I'm tired, so this got a bit rambly, but I hope at least some of this was helpful. Good luck, have fun.