I had to learn through trial and error that 100% fire resistance doesn't protect me from lava instadeath.
You find that unreasonable? Lava isn't the same as fire. Even so, you died and then found out. I didn't test it because I also saw the hint on the loading screen that explained that. Personally, I don't consider that one to be a failure to inform. I mean, some part of the back of your mind had to have thought it may not have worked? I mean, its lava!
That sentinels can see through 5/5 stealth but not invisibility. Had to stumble around the Cyseal outskirts trying to find Aureus' locations, because apparently he is too much of a prick to mark them on your map.
That is for you to explore. This is common knowledge for RPGs(ie from the D&D days and many games that used that system over the years). Stealth is a physical skill, using light and shadows to hide. Those with extremely high abilities to spot details, see at night, etc... (high perception) can see through such. Invisibility on the other hand is a magical means of hiding. Unless one has magical ability to see through such an illusion, they won't be able to detect it.
Personally, I love finding out stuff like this. My friend and I spend a lot of time messing around with different spell, skill approaches, different mechanics, etc... and we have found a lot of interesting things in the game because of it. If that is all laid out, well... it defeats the exploration of options in play.
Even if you did know the difference between that, how would you know if they could see or not unless you experimented? Are you saying the game should just tell you? How would your character know?
As for the locations, those are in general directions. You don't have to stumble around, you just head in the general direction he tells you and you will come across them. If you are expecting to have things like this dropped on your map, well... you are missing the point of this style of game. There is no hand holding and unless the NPC giving you directions knows exactly, all you will get is general directions.
Don't get me wrong, I enjoy the game, but it could be that much better if there was less trial and error reloading.
Nothing wrong with reloading, especially when you are new to the style and genre of the game. I disagree that the issues are simple trial and error to resolve though. I mean, testing and finding out is a huge aspect of these games. If you knew upfront because it was clearly marked for you, what is the point?