Trent Oster: On the PC, we've mostly left the basic controls alone. We've moved a few screens around in ordering and added a number, but the controls will feel familiar to fans. We also brought the key mapping system inside the game itself, so you can re-map controls from within the game. The iOS controls took a few whacks before we had something we were happy with. The first few ideas just did not work, so we went back to the core actions a player performs and optimized around the most frequent actions you perform, such as scrolling the background and moving the party. In many cases, the right option became clear only after a while of playtesting.
Trent Oster: 
If you count the legal wrangling, it is almost three years. Hard full time development is around 18 months. A big part of the work was learning the Infinity codebase and where the dragons were hiding. We did a number of major code passes where fundamental changes were wrought, including the re-working of the entire threading model, a replacement of the majority of the rendering code and a complete replacement of audio, movie and multiplayer code.
Yes, the process could be done on other Infinity games. We plan to use the same codebase for our upcoming Baldur's Gate 2: Enhanced Edition. Further projects will depend on how similar they are to the BG codebase. Icewind Dale is very close, Planescape:Torment is less so and Icewind Dale 2 is pretty far out there.
Trent Oster: Bioware was involved in the legal and let us go spelunking for assets at their offices.
Trent Oster: Most of the code we write is C. The Infinity Engine is all C++. With the proper effort, we were able to make the code very cross platform compatible. We use Visual Studio and XCode as our main tools and we make use of SDL for our multi-platform low level library.
Trent Oster: Yes, we have plans for BG2 and the save games are still compatible and are not platform specific. We'll respect the original design decisions in the game in terms of starting party members, etc..
Trent Oster: We've gutted the multiplayer, and it is better. We hope to continue to improve the multiplayer going forward with matching support, as it is currently just IP connection based.
Trent Oster:
We started with the BG2 UI graphics as a guideline and repainted every single UI screen by hand. For the background and character art, all the source was lost, so we were unable to return and were forced to improve on what was there. We've added the ability to play at much higher resolutions and added zooming support with Catmull-Rom Bicubic filtering to ensure the art still looks good as you zoom in and out. We created the UI with the Retina iPad as a target. Since we are having size issues, we'll likely ship with the iPad 2 UI base and add the higher resolution assets down the road in an update.
Trent Oster: Sam Hulick is an awesome composer. He is a huge fan of Michael Hoenig and really worked to capture the same feel while adding new elements. I think he has done a brilliant job, and I'm looking forward to the fan reaction to the new music.
Trent Oster: We made a list of 20 or so games we thought needed the treatment. Fallout 1 and 2 were on that list, but the ownership situation is sticky enough to keep us away. EA didn't want to talk to us about the Ultima series, so the list of RPGs is getting short.
RPGFan would like to thank Trent for his responses to our questions and his time! You can pre-purchase Baldur's Gate: Enhanced Edition on PC from the Official Website.