This is a low-level change to a lot of our core functionality, but we don't expect that anything will behave differently, but this upgrade will make the lives of our developers easier in the future.
If you care for more detail, though this is completely irrelevant to everyone but me, Foam, and Basilica:
Spoiler:
The ACR does a lot of stuff that the scripting language that comes with Neverwinter Nights can't do. To do these bigger and more-interesting things, we use CLRScript -- because CLRScript is a whole different language, though, it has its own way of turning code into program functionality. The .NET framework comes into play twice in this-- first to turn our code (the literal words we write) into the Common Language Runtime (hence the name-- CLRScript-- which is a step between words on a screen and instructions that are ready for a computer to execute). This first step happens on the build machine (in this case, mine, but when someone tests an ACR change, they produce their own build, where this comes up), and again on the server. The first time that we use a CLRScript component, the .NET framework takes that common language runtime and quickly compiles it down to machine instructions (this is the JIT / Just in Time compiler that gets mentioned once in a rare while). Fortunately, our servers are already up to date, so they don't need to upgrade to use the new hak-- we just put the new version up and the framework is smart enough to use the right stuff.
Our move to 4.5 is especially prompted by one specific library (System.Management.Automation has a wee bug in it), but this is probably a good move anyway. The newer versions of .NET are better maintained than the older ones, and contain a lot of low-level bug fixes to make it easier for us to write out code, though the potential for change is fairly broad. While new versions of .NET don't have bugs the way a new version of Windows would (low-level functional code is more stable than UI code for a number of reasons), there's some potential for unexpected behavior to come along. We would expect to just fix it, the way we did with .NET 4, if that comes to be.
You can now only make tradescrolls from spellbooks that are identified.
Rapiers made out of special materials are now priced as one-handed weapons, instead of light weapons
NPCs who are turned hostile with the DMFI tool no longer auto-attack the nearest enemy (as that nearest enemy might be hidden).
The Will o' Wisp touch attack has a better VFX, which should include a little lightning bolt jumping from the wisp to the target (instead of the previous sparkle that only appeared on the target)
Haven Song was previously not actually making it into the haks, and so all of the claims we were previously making about Haven Song, weren't actually showing up in play. This is fixed now.
