Converting a world from Unleashed (MC 1.5) to Monster (MC 1.6) is basically impossible. Between the massive changes to Thermal Expansion, Thaumcraft, and IC2, a direct port just isn't going to work.
As for a summary of differences (disclosure - I used the 1.6 Direwolf20 Pack, but the mod differences are still relevant):
- Thaumcraft, as you seem to know, is completely different. Research, crafting, infusion, flux, nodes ... all changed.
- Thermal Expansion: updated from version 2 to version 3. It now has its own power system (Redstone Flux) and a few Dynamos to generate that power. MJ cannot power TE3 machines, but RF can be used for most machines that require MJ. Tesseracts are no longer separate for item/liquid/power, it's all in one configurable block.
- IC2: Monster uses the Experimental builds, which show the influence of Greg (from GregTech) being on the IC2 team. Recipes for most things require more steps, and the power system has some quirky changes that I'm not totally familiar with. Making an energy crystal requires 4 diamonds to be macerated, combined with redstone, and then compressed. UU-matter is now a liquid.
- Tinkers' Construct: blue slimes no longer spawn like crazy, only appearing in the presence of the slimy blue liquid found on the floating slimy islands. Blue slime is now a better material than green slime.
Others, feel free to pick up where I've left off.