I like the system in Nahlakh. All spells consist of three magic words and each (or almost) letter of the keyboard produces a different magic word when placed in a certain placement. For example, the letter R in the first slot becomes "Rakh", which is the magic word for starting projectile spells - but you have to learn this from context and the mechanics. At first, you have only a small handful of full spells you get from the game's instructions or rare spellbooks, and you don't have any real understanding of what the magic words in the spells mean. Failure rates for amateur spellcasters are very high, so you're inclined to keep using the few easy spells that you know you _might_ be able to pull off. But nothing really restricts you from trying out any spell words available - it's just that most combinations are a waste of time and your strength (which is consumed by failed spellcasting attempts and restored by resting, which in turn consumes food).
Once you learn a couple of similar spells, like RIF "rakh im fyr" ("spark" - small fire attack) and RII "rakh im iz" ("freeze" - small ice attack), you start to get an idea of the meaning of the magic words, and you can cautiously start trying other combinations that might work. It's not a big stretch of the imagination to come up with a stone-based attack spell once you learn that the "xa" word in the last position from the spell means "stone" - and you might learn this from the priest spell GBX, which creates a stone obstacle in the battlefield. RIX throws a pebble at your enemies. Extrapolating from this knowledge and the spark spell, you can deduce that GBF creates a fire obstacle. Again, however, it's not just a matter of grinding out all of the possible combinations - spell failures have a cost. Luckily, there's a priest spell that creates food - assuming you can figure out what it is and are skillful enough to cast it.
While your skill level grows by casting spells so that eventually you'll be able to cast the easier spells successfully all the time, the more effective spells are hard to get right, so things keep on being interesting. I know that RMF is a strong single-target fire attack, and RMM is a spell that has a good chance of killing a single target (assuming they're not undead, a demon, a golem, or something). RLF is an area-effect fireball, a really good and difficult spell. Should I even try RLM - "death ball"? I don't know if it's programmed in the game. I know that it'll be really hard to pull off if it's possible at all, so it's a high-risk, high-reward gamble - should I stick to something that I know can work? It would be nice to wipe out all those mooks with a single spell before they reach melee distance...