Baldur's Gate 3 by Larian Games

I'd actually say that you won't miss much if you're super thorough and make sure you visit every part of the map. There are some super hidden things that you won't find unless you know to look for it, but those aren't too many.

These are some of the sites I used to help with various things through my playthrough:

Mike's RPG Center (maps and walkthrough summaries)
GameBanshee (PoI marked maps with more detailed points)

I didn't find any decent encounter guides, but as I played on Core rules it wasn't really needed anyway

Oh, and a couple good tips for anyone getting into the game to help with the inventory management issues:

Head to Watcher's Keep early and buy the crossbow that can fire without ammo. Clearing the first level gets you some nice stuff including an ammo belt.
Buy a Gem Bag/Scroll case early on.
A merchant in Wuakeen's Promenade sells a pretty cheap set of glasses that can be used as an identify scroll 3 times a day.
Getting Hexxat even if you don't mean to use her gets you a knockoff bag of holding. You keep it even if you remove her from the group.

These things makes shit so much less tedious.

Core results in pretty much being able to just attack move every encounter after pre-buffing, just with reloads to account for RNG deaths, provided you have decent gear and builds. Unsure about ToB, and I imagine any setting that increases the things that actually kill you (insta death mechanics etc...) will make things excessively annoying.

I didn't know I wouldn't be able to go back to the base game areas after starting ToB. Am I missing out on anything important having not done the following:

Mindflayer Lair in sewers
The Lich quest in the city
Killing the Shadow Dragon
Doing Watcher's Keep outside of the ToB version

The issue is there's never a point of no return warning. I had shit stashed in a container in the city, including things like the entry stone for watcher's keep. Had to edit it into my inventory to proceed. I had assumed that the game just deposited you wherever after killing Irenicus, and having to import your save over to ToB, but it does it for you automatically.

Not really a big deal, it's just one of those QoL things that gaming wised up about over the years.

There are no negatives that I can think of, and many positives. The only real criticisms I've seen about them are some of the new companions are annoying, but they can just be avoided. Dorn makes up for that though anyway.

It's just for the console versions, but yeah, it's neat. $200 is pretty fucking absurd though