Runers is an amazing combination of discovery and rogue-like gameplay. You use 1-3 of 10 different types of runes to create hundreds of spells. Of the 285 spells you can only discover a handful per run, and runs can take hours. In other words, this game's element of discovery can last hundreds of hours.
The spells are incredibly unique and versatile. You'll find that they fit into general categories and serve similar purposes, but that no two spells are the same. You can also upgrade the spells you have created by using additional runes on them. This doesn't simply upgrade damage or cooldown time though, but any of a number of aspects of a spell including but not limited to: buff duration, radius, force, speed, knockback, stun duration, and even "leash elastic." Clearly not all spells will have every one of these and more aspects, but how a spell can be upgraded is just as important as how it first appears.
For me the best thing about this game is that it is a rogue-like with meaningful general progression. Usually in rogue-likes, once you die you start over and very little will have changed other than your knowledge of the game. In this game you might discover a very useful spell on one run and feel great about your progress even without winning or performing well.
A really important thing to understand about the mechanics of this game is the meaning of "discovery." Creating a spell for the first time does not simply mean adding a new "recipe" to your runedex that you could have just looked up on a wiki. You need combiners to create spells for the first time, afterwards you can create those spells using only the required runes. Combiners have another possible use though, in that you can break them to gain experience. I can't stress enough how important it is to be aware of this aspect of the gameplay. If you look through the discussions you will find many, many people who didn't become aware of this until they had put many hours into the game.
I definitely plan on completing my runedex so there's no way I couldn't recommend this game.
I should also add that this game has a pretty cool soundtrack.