I remember liking Witcher 3's. It made the world feel large and lived in. Although I'm not the kind of person who needs to complete everything on a map. I have heard people complain about that
There are some decent ones where you can find fragments of stories told through letters and/or environmental storytelling, but most of the question marks are just mindless monster nests, bandit camps and buried treasure. Skellige in particular is notorious for all the question marks in the water that are just vendor trash flotsam to collect.
In general exploration in TW3 would be more rewarding if the itemization wasn't so scuffed. The only gear worth using is the Witcher sets (which you craft), which really lessens the excitement you feel when looting. There were so many times where I found a guarded treasure, defeated the boss and looked at a cool unique sword, only to realize its stats were beyond atrocious.
Yeah, I think that's why I didn't have an issue with it. I remember only doing maybe 1 or 2 of the barrels in the water in Skellige. I mostly used the question marks as small distractions as I went from one quest to another. I never focused on clearing them out.
You're right that most of the items weren't that rewarding to get. It's mostly just busy work. Hopefully rebirth keeps that stuff to a minimum and just has a large map with cool locations and unique well written side quests. Maybe a few collectibles scattered around the map to reward exploration too.
The first thing I do with any open world game is turn of all map/quest/achievement markers except for maybe the active selected quest. It makes gaming so much more organic. Aso when you do a replay you can still find fresh quests on your second/third plays.