I'll start by saying Zero Dawn is probably my favorite PS4 game and one of my favorite games of all time. I also just replayed and finished HZD the day before Forbidden West released so I remember exactly how it feels and plays. Having said that these are my thoughts on Forbidden West:
I think the gameplay is worse. Climbing, Scanning, Combat are all regressions from the first game.
In the base HZD virtually every machine had different tactics, Guerrilla changed that in Frozen Wilds by making everything super agressive and similar and threw strategy out the window. Forbidden West follows suit, everything is super agressive, immediately charges into melee range, and every fight plays out the same way. Human enemies are terrible because they all wear headgear that making sniping impossible and every fight is either stealth kill or another melee battle. Melee combat is, thankfully, improved and that's about the only part I prefer.
They also give you a larger weapon wheel, but then water it down by having weapons that have a single element or skill. You only had 4 weapons slots in HZD but you had far more diversity in those four than you have in HFW with more slots. I have like 30 weapons right now that could be replaced by maybe 6-8 in the first game.
Scanning is terrible because it last like two seconds (not an exaggeration), so you're CONSTANTLY scanning and it leaves this hideous neon light on terrain if you set the option to keep it on permanently. You also have to scan mobs right after you kill them and by the time you loot an item or two you have to scan again to find the rest. I get that they wanted to remove the pointers from the first game, but I'd rather have them than the current scanning method. You can really tell that all the design decisions were heavily weighted towards pretty images rather than QoL.
Frankly, every part of this game that is better is centered around the graphics IMO. Maybe the story will end up better, but as of right now, 18 hours in, it's a wash. The first game is also more polished, and has less jank. Honestly, if the first game had these graphics, animations, models, I'd take it over this game any day of the week.