Thaumcraft 4 has done a lot of things right, and overall is a significant improvement over 3, especially in its crafting and golemancy systems. I love it to death. Seriously, scrambling around trying to balance things out and keep the infusion going while crafting my Osmotic Enchanter and nearly dying in the process was some of the most fun I've had in 1.6.4. That said, TC4 does have problems, and the problems it has are far, far more frustrating than the problems that 3 had.
- The process of discovering aspects is not intuitive. A lot of people make a thaumometer, scan everything they can, but realize that 90% of the stuff in the world can't be scanned, get frustrated, and give up. Not being able to scan supposedly simple things like wood and grass early on is a problem.
- Impossible research. It's rare, but if you don't know that sometimes you'll get a page that just can't be done you can end up wasting a huge amount of time and research points. If someone doesn't know that you can scan nodes for large amounts of aspects, this can essentially stop their progress in the mod for good.
- Alchemy doesn't have a good way to use precise amounts of essentia, leading to gobs of flux everywhere for the recipes without even costs or convenient reagents. This wasn't an issue in TC3, since a little flux was no big deal. But in TC4, you're rewarded with ugly purple goo that you can't get rid of, and gas that only goes away if you let it escape into the sky.
- Nodes are a bit too rare, leading to frustrating hunts around the world looking for a node with that one particular aspect that you need. The problem is compounded by the fact that nodes only recharge when their chunk is loaded, so that one node you found 400 blocks away that had the aspect you needed will still be drained dry when you come back for seconds.
Thankfully, the fixes for these are relatively straightforward.
- Give a couple of pre-discovered "freebie" compound aspects to the player from the start, like Victus, so players won't be raging about not being able to scan trees and grass.
- Balance difficult researches more towards having large amounts of useless runes cluttering up the page than towards having only just enough active runes to complete. Not only are tighter pages more difficult even when you know what you're doing, they also reward finding red herring aspects much more.
- Allow crucibles to be hooked up to an essentia piping system. Or make a tier 2 crucible that hooks up to piping. Or make an alchemy golem that goes and fetches precise amounts of essentia for you. Something. Also make flux gas dissipate on its own like flux goo, so you won't have to hack chunks out of your ceiling every so often.
- Increase the spawn rate of nodes by 25-50%, do some kind of timestamp checking so that nodes can recharge when the chunk isn't loaded, or make moving nodes around something you can accomplish with a greatwood wand.