I thought as v3 is coming up, I'd share my experience of dipping into v2, if anyone is interested. Short summary of my experience: GT is fascinating, but there are some things that depend so much on luck that they can become frustrating.
1. The Stone Age
I find myself in a scene of breathtaking multicolored beauty: giant blue-barked eucalyptus trees, yellow-and-green vines hanging from sheer cliffs, dense brush everywhere, such a profusion of life I don't think I've seen in any other modded MC biome - that's ExtraBiomeXL's Extreme Jungle (when v3 comes around, I won't rest until I can make my home in a similar place. I love it).
Regardless, survival is the first order of business. Priority 1: make some wooden and stone tools. Wood is everpresent - so much for GT's wood nerf, which I still find noticeable but not critical in this kind of environment. Next priority: find some sheep. Eleven if you can, but three will do if neccessary. Since I can't see much, I climb one the vines to the top of the cliff - hey, a tetrahedrite vein - and look around. There is (normal) light forest beyond this hill, and I see white dots indicating some sheep. Nice, I'm in luck, I climb down and manage to kill 13 sheep. Not only do I now have enough wool for a bed and a sleeping bag, I also have enough meat to last me a while. I go back to my dead-end valley and carve a puny 2x3 shack out of the cliff, with my crafting table doubling as part of the wall. Just in time, it is getting dark. I hate monsters. Really.
Food, at this point, is a pleasantly minor consideration. For now the meat from killed sheep and the occasional apple dropped from "my" oaks will last me quite a while. However, believe it or not, finding the 8 (!) iron ingots I need for a basic set of tools is an achievement. I made myself a set of flint tools as I went to carve my first mining tunnels - I never paid much attention to gravel before - but while iron ore is plentiful, most of if you can't mine with a flint pick. So unless you're lucky and find just the right kind of metal ore, you need to rely on small ores for your first iron, and finding enough of that can take a while. I actually made my first hammer from certus quartz because I had more of that than of any metal, but the file and the saw need metal. It is a relief when I finally have them, since now I can mine most other common ores. I can also make an AE2 grindstone, which is a bit less tedious to handle for grinding up your first ores than GT's mortars. That's another tool I never used in a modded MC game before.
OK, next high-priority target: a water source. Since standard infinite water sources don't work, and EnderIO's reservoirs are gated beyond the ability to travel the Nether and to make steel (which you need for EnderIO's alloy furnace, which makes the fused quartz), my only option is the Railcraft water tank. For that, I need - slimeballs. I should admit that I almost stopped playing at this point, for in my experience, slimeballs are a mid-game resource. I never have them early, and having to hunt for them is a major, major frustration. In most packs I can fly before I find slimeballs, which means that my usual sources are TiC slime trees which of course are absent from this pack. Since exploring underground is depressing I go on several exploration tours of the surface, hoping to find some swamp-like biome. What I find: two villages with some nice loot - no steel ingots unfortunately, but thaumium ingots, some gold, 12 dark steel ingots (which I still have days later because I can't use them for tools, grrr....) and two steel swords (away with you to the swamp, flint sword). I also found a stargate ring component...WTF? No slimes so far but across a lake there appears to be some swamp-like terrain. After spending my night in the village, I explore that part, it looks promising. Another village with more interesting loot - more thaumium, still no steel, and lots of rails - and an aluminium vein. I spend the evening sitting in a tree until the monsters come out. Yay, slimes! Unfortunately, lots of other stuff, too, but I manage to kill enough slimes for 33 slimeballs before I have to run away from the mob of mobs.
Next order of business: a tin vein. Those prove considerably elusive but I manage to find one eventually by looking at the side of hills. This takes almost as much time as the hunt for the slime. At this point, I am considerably frustrated. Having to spend so much time hunting for resources is giant PITA. Forget GT's complexity, I can deal with that very easily. Forget early technological processes that take forever to complete, I have a lot of patience if I know there will be a nice outcome eventually. Things that depend on luck like prospecting are, and will most likely remain, a major point of frustration for me. This is compounded by yet another expedition, this time for just two diamonds I want to have for my first machine... Another real-time day goes by as I find a dozen more iron veins and some other interesting stuff I have no use for at the moment. My first small diamond ore block doesn't drop a diamond but only dust. At this point I almost give up yet again. Once you find a vein, actual mining is much less of a pain than in vanilla MC - the veins are usually big and last a considerable time, and they're convenient to mine manually since if you stand on the lowest level, you can usually reach the highest with your mining picks. Using a "core-sampling" strategy for prospecting - mining 2x2 shafts down to bedrock in a 50-block grid - will let you find something interesting almost everywhere, but if you're looking for something specific that might not alleviate your frustration. I am going about this very systematically, including building walls in shallow water so that I can dig down there. I find silver and lead, cobalt and nickel, lots and lots of redstone and enough iron to build my base from iron blocks should I ever want to do that, but no more diamond ore except a random small ore that dropped a diamond and a flawless diamond (which equals two regular ones). I have what I want, and some time later I find an actual vein, but that was....thoroughly unpleasant.
2. The Steam Age, part 1
Now at last I can start doing what I started this pack to do: build machines. I spend some time mining copper and tin, and I move out of my little shack and build an actual house. Nearby there's an expanse of desert so I'll never want for sand to make into glass. None of my houses ever lacks windows - someone should ask dw20, btw, if he knows about the concept. I need to fell one of the giant eucalyptus trees for space. That takes quite a bit of work but provides me with lots of saplings and the wood for my roof. A roof made from blue wooden stair blocks. Nice. On top of it goes the water tank, and an adjacent area of the house retains a flat roof where I put some sand to plant cacti. I'll need those for some BC fluid pipes. I have also spend some time manually farming trees, and make charcoal to cook up a lot of stone, and bring some spruce saplings to plant in groups of four in another cleared area beyond my house. They will give me several stacks of wood in a minute. The drawback: each time that costs me an iron axe - at this point, 5 ingots.
Grinding up tin and copper in the grindstone is quite a bit of work, but as I said, I have patience if I know the outcome. No matter. The work is almost meditative at times, and at last I have enough bronze for a small coal boiler and a steam macerator. I make a water pipe down from the water tank on the roof, and a steam pipe to my machine. Ugh. Early BC pipes are primitive, but then I am just out of the stone age. The steam macerator takes 40 seconds to process a block of ore, and at this point I have to macerate any crushed mixed ore again to get at the dust which can be smelted to the metal. I could use the hammer for that, btw....but I have better things to do. I manage to automate the macerating using BC pipes, a redstone engine, a hopper (10 iron ingots apiece) and some chests, and cheat a dimensional anchor in. As I said elsewhere, I think that technical game issues like chunkloading should have no effect on world simulation, and for that reason I find nothing in cheating that item in and setting the config to not using fuel. Now I can go prospecting while my single machine is doing its stuff. That's quite a bit less frustrating than before since I know something useful is happening while I trudge along in those depressing rock corridors. I actually manage to find a diamond and graphite vein. Just my luck, though: it's intersected by a giant ravine and most of it is air. Still, I get a stack of diamond ore out of it. To my disappointment my Fortune III-pick made of Thaumcraft water shards has no effect, I just get the ore, but still, this will last me a while.
At this point I should mention that diamond, obsidian and some other stuff needs a level three mining pick. The easiest way to get that is by using Thaumcraft shards at pickaxe material, which are omnipresent, but elemental picks need a thaumium rod as a handle and you might not have that. Elemental picks also have low durability. The next best way is to find a cobalt vein. Cobalt ore can be mined with a level 2 pick, can be macerated and smelted directly to cobalt, and tools made of cobalt have a mining level of 3.
(to be continued)