Apart from all the bugs, underdeveloped and convoluted settlement construction and management system, lack of interesting locations and world building, and retarded AI, the biggest thing wrong with the game is the ending.
The game literally forces you to murder everyone of the opposing factions.
No matter how high your Charisma stat is, the game refuses you to give you a diplomatic option, which is especially infuriating between 2 of the factions, where all you would need to do is to slap some sense into them.