I didn't particularly like Interstellar but seeing it in IMAX was an incredible treat. I have no doubt that the same will be true for Dunkirk.
This. Interstellar in IMAX is still probably the greatest theatre experience I've ever had. The quality of the film is debatable (I personally loved it) but you can't argue that its scale is magnificent, doubly so in IMAX. Dunkirk will be the same way, although it doesn't seem to have, based on the reviews thus far, the glaring plotholes that Interstellar had.