Few days ago I was this close to dropping the game,I think the feedback could be useful so here are the sources of my frustration.
Enemies hidden behind environment – I’m not a fan when loot is hidden this way but argument can be made that finding it can be exciting and you don’t need to find all the loot to progress the game. But ask yourself what is gonna happen when player gets ambushed by enemy he didn’t see ? Yup a load, that's fun eh ?
Extra fast enemies – if you don’t want given enemy to be ambushed, fix their location in such way that they can’t be or make them unable to be ambushed in some other way. This is nothing but invitation for save scumming.
Hidden passages – not the cracks you need to blow up but the holes in the ground that you need to walk into to discover them. It is one thing when you expect there is a passage and you look for it it is another when you casualty walk around and then suddenly screen changes. I had three of those situations that I walked into a passage and that begs a question how many have I missed. Now ask yourself what type of gameplay this promotes? Face checking like a lunatic every cranny that is obscured by environment.
Why do you think enemies got levels in RPGs? (those that don’t either employ “you can finish game at lv1” approach or have some other way of communicating/controlling difficulty). In this game there is no way of telling how hard is the enemy other than saving and face checking it. There is bestiary but it is inaccurate and you need to fight the enemy first to have info while its not accessible in combat and you can’t run away from fights.
All and all I feel like the game got many outdated design choices from times where one game would have to last you for months. That is no longer the case, I don’t need/want to be playing same game/ piece of game until I get things right, that is not fun. Also do not mistake it with me wanting to game to be easy, I enjoy challenge. Read on the difference between challenging and punishing games, SKA is more of the latter.
If you refer to semi-hidden enemies at the start, I don't see the big problem. Yeah, you need to look closer sometimes, but you can spot them, so it's not a mess of forced ambushes you only can circumvent by save-scumming like you describe. In many playthroughs I didn't encounter a single enemy you literally can't see. Every fast enemy can be ambushed by spotting them beforehand and circumventing them, or through flash bombs (will elaborate on that later). Alternatively there are also slow enemies which can be circumvented by kiting, etc. Yes, it's possible to be caught of guard and you have to reload if it kills you, but it happened only a few times to me. Where save-scumming for me came into play is stuff like collecting gold for the Avian, but you can also kill it through other means if you want to.
Same goes for hidden passages - There are a few that are difficult to spot but for the majority of the game, the maps are also intuitively designed in terms of what can be looted and what can't be. And where to maybe look twice.
The point about difficulties not being communicated beforehand is fair, I would say a rule of thumb is that the order you receive quests can be a rough guideline. With the exception of optional dungeons like underwater and mount firestorm, those are basically ongoing challenges you just need to check in from time to time how things are looking there. SKA is not a game where you can just stat check against your opponent in order to weigh properly if you can beat them, many enemies can be beaten with proper strategies even with the stats not being that high. Like for example how Lightning Sword completely changes the difficulty against most mobs in Draknor Fortress. I think it makes more sense that x mob is always the same, so at least you know their weakness and how easy it was to beat them with x approach.
Elaboration on the bestiary statement would also be interesting, because it is literally not inaccurate? I wish it would contain a bit more information on skills specifically (though you can look them up on the wiki), but the information you get is correct.
And you can run away from fights using flash bombs. It's not something you should be doing for every single fight, but you can splurge gold on a decent bunch and use them when you feel its necessary - In fact, flash bombs allow you to back attack enemies you can't back attack otherwise so it opens up more avenues in that regard (and also why the game becomes imbalanced if you could abuse such a feature)