Well lets be honest here; you can always go back to playing 2ed and 3.5ed. 4ED has changed things alot, but dont look at it as an old game set progressing... look at it as a new game set completely. Just look at the books and all the changes to the storyline and setting... its not just the 4ED rules that changed.
The graphics are fantastic and the engine is very smooth actually. I recommend you reset every single video option; (even if its at the setting you like) you may have run into a bug. Also ensure, you graphic cards settings in your NVIDIA or AMD Control panel was not change recently.
Although I am in no way an expert in the legal matters here.... as long as you aren't charging for money; it maybe alright. However I suggest that you change the story just enough and character names, so that its not out right copying.