Howdy...
"real" IMAX theaters as referenced by that linked article are FILM theaters that actually project 70mm/15 perf film on to large screens. Up until about 10 years ago, that's the only type of IMAX there was. Then they got greedy.
The first step in the dumbing down of the IMAX brand was to retrofit an "IMAX" theater into what was formerly two standard size screens. That may give you some room for a wider screen, but you still don't have the height. Many of these type of theaters may have screens as skinny as 2:1. They may be projecting 15/70 film, but there's little point in seeing The Dark Knight Rises in one of these retrofitted screens, as you won't get to see the full frame IMAX scenes full frame! (most of these theaters have been converted to digital by now anyway)
Then came digital. IMAX was in a real rush to get into digital before anyone else. They spent millions of dollars trying it as early as 2000. That original system failed, but eventually they got one that "worked". Alas, it's only 2K, and of course is limited by the chip size/shape to a 1.78 aspect ratio. (and don't let the two projectors "sub pixel aligned" BS fool you. It's 2K and it looks like 2K. The two projectors give them some more brightness, but the resolution simply isn't there.) The screen sizes are considerably smaller too, as there's simply not enough light coming out of the two digital projector to fill a huge 100' screen like a film projector can.
Dome theaters: Stay away. Yes, they're projecting 15/70 film, but through essentially a fisheye lens and wrapping the image around you. Great for the .0001% of films which were shot specifically for this type of presentation, but possibly the worst movie going experience you'll ever have if you try watching a traditional film this way. You've been warned.
Sadly the days of the huge screens showing 15/70 film are coming to an end. IMAX is converting theaters to digital at a feverish pace. Keeping up with which theaters are showing which format is not easy. I suggest you call your local theater and ask what type of "IMAX" their theater is. (if it's less than 10-15 years old it's very likely "LIE-MAX".
That said, IMAX is now working on a new digital projection system which promises upwards of 6K and enough light to fill the huge screens again. So perhaps, just maybe, IMAX can go back to being a premiere format worthy of paying a little extra for. Right now though...save your money unless you're lucky enough to live near one of the very few original huge 15/70 film theaters that are left.
It's worth noting that IMAX recently changed their slogan from "Think BIG" to "IMAX is believing". They don't want you thinking "BIG" at all, as the vast majority of their theaters aren't "big" anymore. Further...they don't want you "thinking" at all. Just "believe" you're getting a vastly better experience.
