I have never used the 3D. It works GREAT in HD. One caveat: You do NOT want to view it in a well-lit room. You need blinds on your windows. I have it in my bedroom and it works GREAT. Think of the environment you'd want if you were watching a slide show or 8mm home movie on a projector screen.
Yes, it is an HD TV that has the capacity to play in 3D. You don't have to use the 3D feature at all, but its there if you want to. I've used the 3D and its fantastic. I just prefer to watch my movies without it.