Check the interview there, but here're some snippets:
RPGWatch: Were you nervous about changing anything in Planescape: Torment? I know you already worked on Baldur's Gate, which has a bigger audience, but Planescape: Torment leans more heavily on its writing and overall tone. It carries the game to a much greater extent.
Alex Tomovic: As the Project Lead, I defined the vision of PST:EE long before production and development started. The goal of the Enhanced Edition was to deliver the canon Planescape Torment experience to modern devices, without altering any narrative or gameplay aspects of the original. Therefore, you won't see any new companions, quests, areas, races, classes, kits, items or spells in PST:EE.
RPGWatch: What were the main challenges the team faced with updating Planescape: Torment?
Scott Brooks: One of the biggest challenges was that Planescape Torment was the first time another team tried to build a game in the Infinity Engine other then Bioware. When going through the source code you could see how two similar features were added in entirely different ways. This can happen when you are attempting to learn a new engine, and develop a game at the same time. Planescape also solved some of the same problems BioWare went on to solve in later versions of the engine in different ways. Sorting out these differences and reconciling them was a big challenge. Another big challenge was implementing the cinematic spells. These are all hardcoded to act a certain way, with certain timings. Some of the spells, like Celestial Host, take 90 seconds to cast, so when you're trying to debug they can be quite a pain.
RPGWatch: What did you learn from previous EE releases that you used in this release?
Phil Daigle: We've mastered the art of walking that fine line between curation and improvement. Classic games are near and dear to the hearts of many gamers, and so when you adjust or change something about that game you need to present an extremely clear and compelling case as to why you're doing it. I think we've accomplished that goal with all of our improvements and enhancements in PSTEE.