Unity C# question

I am new in Unity, but I am thinking about move my game project from XNA to Unity.

My question is:

In my XNA game project I’ve got my game world representation in C# and it’s independent from XNA. It uses the .NET 4.5 classes like System.Collections and similar. Only my GUI is XNA-related.

Will it be possible, to move the whole C# code that is XNA-independent to Unity, and just create new GUI in Unity, or I need to rewrite my code to make it compatible with Unity ?

Regards.

As long as the C# code does not have any XNA related functions or classes in it as you say then it should work fine. Unity uses normal C# and have not modified it in any way. I came directly from XNA myself first time I used Unity and there were no differences to the C#. You will need to use the Unity API for the unity specific functionality of course though.