Like: open world combat where you can plan and use geography to your advantage.

Hate: Inventory management

Guild Wars 1

Having a character of one main class and a secondary class that could be switched at any time between any of the 9 classes.

8-slot skillbar with one heroic skill that could only come from your main class.

400+ total skills in the game.

Plenty of room for you to make your own homebrew builds, and some classic builds that were outside the box:

The assassin that used a staff (assacaster), the ranger that used necro skills to touch people to death (touch ranger), and the 55 monk, which had almost no hp but so much healing it was hard to kill.

It will always be my MMORPG because of the character design.

I really appreciate that in MGSV when you move to first person view for iron sight aiming, the controls change to properly feel like a first person shooter. In contrast GTAV and RDR2 also have first person modes, but you still have the character movement of third person and it feels very wonky.

I hate the overwhelming number of currencies and crafting supplies. I shouldn't need to have to gather so much of this thing and so much of this other thing (neither of which are labeled clearly, what they are and how to find them) to craft things. A small number of things makes sense, e.g. metal and powder to make ammunition, but when this potion requires 5 different plants and that potion needs 7, only some of which are common between them, it's an unnecessary time suck.

Then, when I have an abundance of various supplies, I have to go to the blacksmith to repair my armor, run over to the jeweler to craft bigger gems, then go to the chest to stash things, go over here for various upgrades, and over there to craft the next potion I need. Why can't all these things be in one place or at least right next to each other instead of scattered all over town?

Having well placed saved points and QOL features is absolutely amazing. I'm not interested in spending 10-15m running back / repeating myself just because the save progression system is rubbish. A lot more developers are more respectful of your time in that regard so it's a great improvement

Not really a game mechanic by definition, but I hate forced PvP in open world/MMO style games. Even survival games, where one could argue it fits.

I won't buy a game if they do this, so I guess in that sense the PvP is a choice.

While I don't play the actual game, I am a massive fan of the Escape from Tarkov inventory system. Its extremely detailed; a totally unreasonably detailed system for how every item fits into or on every other item. I've watched a few dozen hours of the game just looking for how people manage bags within bags within bags, within bags. I love how simulator-y the inventory is. Normally I hate that, I like sortable menus and proper categories for lists of my items, but wow is EfT's inventory something that has really captured my brain.

Hate: Tapping, quick time events, looting animations, long loading screens especially when you're expected to die often, game taking control away from the player or excessive input latency, long NPC expositions for fetch quests.

Love: addictive gameplay loops that are borderline checklists but fun (Far Cry, Days Gone hordes, Ghost of Tsushima camps etc.), environmental impact like in Death Stranding/reactive NPCs like in Bethesda RPGs.

Love: weapon durability so long as it’s paired with weapon building and leveling systems. I like that I can’t ever take a weapon for granted and that I can’t hack and slash without thinking. I have Dark Cloud in mind as I’m writing this - it was easily my favorite weapons system I’ve ever played, and it always kept me on my toes. It’s a kind of stress I appreciate because I have some measure of control over it as long as I plan and slow down a little.

Hate: timed anything. Way too much pressure, and it pushes me back towards going faster and not thinking so I can beat the timer, which I don’t like. I especially hate it because I primarily play turn-based JRPGs to get away from having to worry about timing and to be able to play at my own pace. If I wanted to do time-sensitive stuff, I’d play an action game.

I absolutely loathe double tap to dodge mechanics.
Terraria does this, everyone who played it with me thinks it's reasonable to fear accidentally dodging into an enemy when trying to walk slowly with a keyboard.
This is 10 times worse on controllers, because dodging just becomes irritating and janky as fuck - if I need to dodge a bullet, I don't want to fight the kinetic energy of my finger for an entire fourth of a second and hope I am fast enough.

Love - auto health or shield regen. When I first experienced that in Halo it made me instantly hate other games that didn’t have some form of that mechanic.

I hate managing health inventory items. It breaks gameplay flow with tedious bullshit that isn’t nearly as fun as focusing on the a combat mechanic.

I love mechanics that add another dimension to a level or stage, like Titanfall 2's time traveling or Duke Nukem's shrink ray

Collecting hidden items. Ever since Assassin's Creed 2 with the fucking feathers, I have hated collecting hidden items. Especially when they gain you absolutely nothing except an achievement. It's like they are trying to artificially increase the number of hours played.