Overall GREAT. Saw Oppenheimer 70mm. Here are my personal views, and i'm fussy.
Location - Super easy to find, basically can't miss it, 5min from Waterloo on foot. First impressions, clean loos and some refreshments available, nice foyer. Inside the theatre, OK - nice seats, whatever the price range, good legroom whatever the price range (I'm 6ft) and not as steep as some say. Ive been in much steeper Imax's, with much less legroom. Picture and sound quality, good and immersive, but not as high as was expecting. Im an audiophile. Screen size is not as large as was expecting. But I think this was because I sat in VIP section. Big Fool. Basically a chop. Price, a bit steep but hey movies are comparatively overpriced now anyway. Right?
Seating. The MAIN point for me was where to sit. As this is personal to everyone. I favour privacy over location, most of the time. I sat VIP on the side, on the isle, with two seats empty next to me. I moved one further in as fast as I could. However here at IMAX, I would say privacy is a moot point due to the way the screen is curved. You need it wrapped around you. Seating plan is spacious and big enough to not be bothered by the person next you (its not the tube or the train you took to get there) IF they are normally proportioned and don't have too many snacks or talk too much or fiddle etc etc. The VIP area does flatten out at the top and you can see the whole cinema, the whole screen, and it has a bit more legroom. However, it also has the loos at both exits, which are at the top, and you can see all of the lighting which stays on during the show. It's a commanding position worthy of your greatness. But i'm not a ships captain, I want to be in the engine room sometimes. If you sit at the end of the row there are these hand rails which sit in your field of vision and you are aware of constantly. Disclaimer - for the elderly, people with vertigo, the blind and people i'm unaware of and/or who have h&s in their job portfolio.
Recommendations. IF you want to experience the theatre by seeing the whole thing and the whole screen, like you would watch a TV at home, and see all the staircase lighting, and have people going to the loo during the show, then the expensive seats at the back are for you M'lud. If you want to be surrounded by only the picture (and not by stair lighting and handrails), and you may have to move your head a bit to see some elements of the picture (like being inside the picture), and surrounded by sound (but...also other people) then the cheap seats are for you. The lower you go the more you have to look up, but the seats allow you to rest your head easily. Stay away from the sides, it's too angled, stay away from the edge of any rows, the hand rails are annoying in your field of vision along with stairwell lighting for the blind. And you will go blind looking at it.
Cheap seats close as possible to the middle, lower or higher - it's up to you. Enjoy.