Having used mine for 2 days now, here are some thoughts (not ranked by significance)
1. Yes it's light when you don't have a case and a screen protector on, after using it with the official silicon case and applying the screen protector, single-hand use still feels heavy. I can't imagine the Pro Max users' feelings.
2. As a first-time Pro Max (size) user, the battery life (on a new device, restored my 13 Pro backup, running iOS 16.1 beta 4 --- that's what MacRumorians do right lol) is superb. I have used it for a day (from 10 am, 100% charge) and there is still 50% left when it came to 00:00 the next day. As of the time I made this post, the battery life is at 45%, I hand calculated the screen on time total which is an amazing 351 minutes (~5.9 hours).
3. I DO MISS THE ULTRAWIDE CAM with Auto Focus on my 13 Pro. The autofocus-enabled ultrawide taking closeups and macro shots are something you'll miss if you have used them once.
4. ProMotion, it's good to have but I don't miss it much as I do for the Ultrawide Cam with AF.
5. Gaming without immediate brightness drop on the go (playing Genshin @ medium settings, 60fps), that's nice.
Anyway, I would recommend anyone who would like to give the Plus a try the following
1. Get a durable case, for the protection of the frame, aluminum is scratch resistant but not drop-resistant ( I have not dropped mine but I remembered how my iPhone 5 dropped and bent its aluminum frame)
2. Wait for a discount from a reputable seller other than Apple? The official price is pretty hefty for its features IMO.