As a total overhaul mod, you need to lessen your expectation that you know how things work in vanilla Minecraft and other mods. Be open to investigating how things are done in GT.
You need to become good at sleuthing through NEI, because there is little documentation other than the in-game recipes and books. Take notes. Read on the forum. Ask questions on IRC. Eventually you’ll find most everything is remarkably consistent and reflects real world physics.
GT is less about multi-function magic blocks than having discrete components to build your own systems. In game interaction with block faces is prioritized over GUIs. Smelting is a great example. In Tinker’s construct you build a cute multiblock smelter, which then operates pretty simply (lava and ore in, ingots out). In GT you build a heat source (burning box, gas or liquid, electric heating element, heat exchanger, etc), fuel it, and then put a crucible on it (clay, steel, up to exotic metals). Then you have to manage the temperature by material or it explodes. It’s up to you how to get the molten metal out of the crucible into ingot molds, etc. There are multiple tiers of heat, of temperature, of materials that must work together.
It’s incredible if you’re into automation, games like Factorio.
My mod pack (Devouring Darkness) and matching server is a hardcore horror survival GT pack. Early game you literally are in the stone age, and progress up through bronze, iron, and begin to make machines, early power, and automation. It’s such a smooth tech progression. I only added the overwhelming odds, starvation, and a touch of magic.
I’m still learning more about EU power sources, integrating GT with AE2, and scaling up my base. It’s fantastic. It’s certainly not a mod you can “beat” in a few days like TE.
Some other reading you might benefit from is my DD guide, which links to other GT pages: Guide
EDIT: Make sure you quickly create a GT Magnifying Glass in game. Many of the blocks that have no GUI will give you feedback in chat when you examine them with the glass. Hoppers show item counts, Dust funnels show their configuration. Pipes say what is in them, etc.