This game... is frustrating. It is frustrating by design. First off, it's a great game if you like HoMM-style tactical combat in a fantasy setting. The graphics are nice, the setting is okay, there's a story that guides you through the game and the combat mechanics are excellent. On top of that, the game runs very smoothly on my 5y old gaming laptop (aside from a rare crash).
That said, it taunts
you at every step. With a minimal grasp of the game, you can get far without much trouble [on normal difficulty]. You can beat most yellow or lower difficulty mobs without significant losses. If you combine some of the more interesting spells with a good army setup and decent equipment, you'll be winning most battles with barely any losses at all. However, as you can only bring backups for two unit types, any time you lose another type of unit means running back, or fighting at reduced strength (generally not a good idea). If you level up, you can carry more of each unit type and... you'll be running back.
On top of that, the game has a built-in achievemnt-style "Medal" system. For several types of actions, you can get a medal if you perform them a number of times, which provides a passive benefit. For example, using 50 defensive spells grants 3% damage reduction for the rest of the game. And, of course, a medal for zero-loss fights. And the reward is great, especially early on.
The game doesn't punish casualties, but makes them annoying enough for you to obsess over zero-loss fights. A Very Weak mob with ranged units can still kill a weaker unit. Sometimes you have the option to skip Very Weak mobs, giving you the exp and gold without fighting. However, you're not grinding for your levels this way, so you'll be tempted to fight them anyway. But a Very Weak mob with ranged units can still take out some of your units, possibly forcing you to backtrack. Ultimately, when you spend 5 full minutes thinking "Should I fight this Very Weak mob?", you have to wonder whether this game is doing something horribly wrong or horribly right.
The game does provide all the tools required for drastically increasing your odds of zero-loss fights, by means of interesting spells and units. However, large portions of the scrolls you find are randomly generated. In all my King's Bounty games, I've never found a Summon scroll at a relevant moment, which are critical spells for the Mage/Soothsayer class. And that gets frustrating.
Sometimes I feel like this game is a psychological experiment. It's not about the battles; it's about you facing your fear of losses, accepting imperfections, letting go of your achievement-lust and just playing the game more casually.
Or maybe nobody bothered to playtest the game without cheats.