This is a great game. It is long, full of secrets, fun, cheap, DRM-free. I played it with full motivation for more than 19h. You should definitely buy and play it.
Nonetheless, I can’t help but feel that with relatively little effort the game could have been significantly better, so I am going to focus on a few weak points in this review. The good points have been mentioned enough in the other reviews.
Visually not enough diversity: There are only three tilesets. One of them is even used for ~60% of the game. That gets boring very quickly. There should have been two more tilesets; one of them could have been a temple tileset, given that three levels of the game take place in temples.
Story: There is almost none, and that little there is makes no sense whatsoever. Given that the story is told mainly through text, they could have added an interesting story with almost no effort.
Some of the enemies are ridiculous, for example: Giant, glowing, green blobs of slime; T-Rex’s; something resembling a companion cube.
Interface:
No quick belt for potions etc.
No quick save/load
During time critical battle action you need to use the right mouse button (where you have a weaker finger) at lot more than the left mouse button.
The mouse axes for freelook are strangely inverted. You can change this in the settings for the Y-axis, but not for the X-axis.
Gameplay: Most of the time the game is very fair; but there is a number of exceptions. Some puzzles are unfair in that the solution makes no sense. Some are buggy; there is one where you need to throw a stone, but only one of the two ways to throw stones that exist in the game will work. Sometimes the game does unfair spawning of enemies behind you while you are stuck in a dead end.
Lots of walking: There should have been a quick way to go back to earlier levels, e.g., teleporting to already seen Life Crystals.
Splitting the party: Would have been a good addition, e.g., to make the assasin skills of the rogue more useful.
