This mods adds content for players who decided to spare Solaufein's life and let him escape. That means that your decision in Underdark actually has a consequence in the later game. I think it's a pity in original BG2 your decisions in Ust Natha don't really matter in the later chapters. When Solaufein returns to you later, after escaping Ust Natha, he tells you how grateful he is. Eye for an eye, and friendly arm for a friendly arm - he tells you about a new place, where you can ask for help with getting your soul back. Mod includes 6 new areas, 21 new items (2 of those are available through Cromwell) and obviously some new quests - it's up to you if you wish to complete them or focus on real quests and get your soul back. On the areas you may hear new music themes.