Going tonight... From what I've heard, it's better than TFA, but... that's about it.
Dolby 2D is actually fantastic, but, for some viewings IMAX is better.. an example would be Blade Runner. Simply put, most Dolby (Atmos) theaters have the sound up TOO high, and I know that sounds crazy but, with the way Atmos speakers are setup, it's simply too much audio and bass. But, for a movie like Dunkirk, unless you're talking IMAX 70mm, then Dolby would be better since it's more atmospheric.
If I were going to see a movie where I care less about picture quality or the atmosphere created by the audio engulfing me, then I'd pick IMAX because of how the theaters are setup; I find the seating to be more comfortable in general and it's simply a pleasant all around viewing experience. So for a psychological thriller, etc, I'd go with IMAX.. almost every time.
If I were to pick between the 3 for Star Wars, I'd go with Dolby if it's for 2D, IMAX for 3D. Dolby has deeper blacks, and higher resolution (8k effective display) and you can generally tell the difference given the viewing distance. IMAX looks stunning, but, Dolby looks better on average IMHO.