I see two primary reasons people dislike TC4:
-It has the worst default configs I've seen in a major 1.6 mod. Natural Taint spawns are incredibly common, nigh-unstoppable and force you to rush for expensive purification tech. This could be fixed by making Taint a real biome, much like how Magic Forests spawn, and removing spread.
-Research is an absolute pain after about 2 worlds, and the 1st world is also painful. This could be at least improved with a config setting making all researched aspects infinite and greatly buffing the Deconstructer.