I want to see Project Hail Mary and I mentioned to my wife that I might want to see it in IMAX. Of course she asked me "what's the difference", and my initial thought was "bigger and better". But is it?

I don't want to spend a ton of time on this, and I'm having a hard time finding actual specs for screen size. And local theatres say they have "Premium Large Format" screens, which is pretty non-descript.

So is it a better experience in IMAX? The cost is nearly the same.

The IMAX theater I used to frequent when I lived in CA was a real, honest to goodness, classic designed/purpose built IMAX theater with the steep rows of seats, and a screen approx. 90'X50'; standing in front of it and looking up is like a 4-5 story building, it was gigantic. Most of the films we viewed were from IMAX film projectors, not digital. For our family, paying extra was well worth the surreal visual and audio experience. If there was a movie we wanted to see as a family and it was in IMAX, we would choose IMAX. Every Chris Nolan film we saw was in IMAX, including Oppenheimer which had a limited run in a few cities in IMAX film. But then there are theaters that would advertise as "IMAX" and it turns out to be a retro-fitted multiplex piece of shit with a small screen and enhanced digital projection.

If cost is nearly the same, yes see it in IMAX.

There are a variety of IMAX theaters, some better than others.
The best I have seen is in Pittsburgh, it extends over your head and wraps you in a total encompassing experience.
Many just have large screens, and lack the immersion of the Pittsburgh model.

The short version is if the film says "Filmed In IMAX" see it in IMAX no matter what. The film will either have scenes that will cover the whole IMAX screen or the whole movie will cover the whole screen.

After that, it depends on the screen. AMC is the big one in my area, but most of the IMAX screens are still using Xenon bulbs in their projector while the Dolby Cinema uses two laser projectors to give you a much better image and also gives you better sound than most IMAX theaters. There are "IMAX with Laser" screens that will match the screen quality, but not every theater has one.

4DX and those that shake your seat of blow air on you to "simulate" putting you in the movie are a waste of time and money.

I learned here when we were discussing F1 The Movie that there are different formats of IMAX.

IMAX 70mm film (the original and true IMAX)

IMAX with Laser (sounds close)

Digital IMAX (aka LieMAX)

The latter is what most screens/theaters are going to be unless you specifically seek out a true IMAX theater. It's still way better than regular film, and the audio is going to be better as well.

They are capitalizing in all venues on the name and expectations of the original.

Unfortunately for most of us, Digital is all we get without a hike. Closest to you is....Dallas.

Hail Mary in IMAX 70mm

Cost was about the same so we saw it in IMAX. Screen was pretty big, and taller format. Sound was pretty good, but maybe just extra loud. It was arguably not a better experience. Plus, the seating was pretty old school- not the oversized recliners like in the newer theatres. Won’t be doing that again.