The biggest differences between now and then are how it is possible to allow players to use ground, cover, facing, and stuff lying around to your advantage, (or detriment in the hands of the enemy). This in turn allows for greater tactical thinking, deeper strategy and more involving and realistic combat.
I personally think Larian is quite wonderful in the way they tackle encounter design. Smarter players who are willing to stop and think before acting are usually rewarded by using cover/high ground and whatever is laying around handy. Warrior characters have to be very mindful of their feet, while magic uses generally are rewarded if they carry teleporting type spells that allow them to avoid trouble and control the ground they find themselves on. It seems to me Larian has slightly "helped" the warrior classes because of the nature of their need to traverse hostile ground more than the ranged classes need to. Which, is just smart. This sort of problem doesn't happen often in the more abstract pen and paper world.
You are right in theory but your description doesn't match with what happens in game actually.
- There is no cover mechanic implemented. People who critizies high-ground often suggest implementing proper cover mechanic as a solution.
- Facing mechanic is a stub. In turn-based game you need to allow change facing as a reaction. That would open an actual tactical challange and people critizing currect backstab rule are suggesting it as a solution
- Surface effects are more or less accepted here, the consensus is only tone them down a little bit, especially with cantrips and review the interaction of surface damage with concentration on spells
- Repetedly using high ground/back stab with every class I really don't feel smarter. I feel stupid.
Poeple are generally OK with added verticality, facing and other stuff but the current implementation is just bad
and it's done very insensitively. That's what people are actually critizing here. To make it better and more in tune with 5e rules.