I'd love to see more games use a system like this:
Basically, you have a ton of different stats. Depending on what character you are, you have different stats. Such as mages have a few different magic attack stats that fighters do not have, while fighters have a few different, well, fighting stats, that mages do not have. Then there are the stats that everyone has, such as Perception (ability to see those who are hiding or see farther away), Lockpick, Immunity (lower damage from magic attacks), etc. Then there are a few primary stats, such as Strength, Agility, Wisdom, Intelligence and Braveness. These stats, when raised, modify the secondary stats, like +1 for every 5 points, along with make the character overall stronger. These stats cost more, too, though.
So you have your primary stats that every class has, then your secondary stats that all classes have, and your class-specific stats. Raising stats is not based on level, rather then it is based on Experience. So you are never forced to wait to level up to raise your stats, which I have always thought was a completely retarded method. Your level is just used as a generic value to how strong you are, and each level raises your health/mana a bit. Each time you raise a stat, it exponentially increases in cost. So to raise it, it may cost like:
And so on. The reason this method is so good is since there actually is a difference between someone who just hit level 100 and someone who is almost level 101. Also, you dont have to wait until you level to become stronger. It also allows you to open up to having tons of stats, since who would want to waste a whole point in Lockpicking when they could just raise Strength, which will be better for them in the long-run? It also allows players to create their own very unique characters. Games like Diablo, there is not much diversity in characters - there is a few best spells and best skills for every class. Most characters are nearly the same, except for maybe a Sorc might go for Ice attacks instead of Fire attacks or something, which is really not a significant difference.
The only real problem with this method is that you are pretty much stuck with the same spells/skill throughout the whole game, which can make using them pretty repetative. For the little rpg I am making, it uses a system just like this except for instead of raising skills/spells individually, it will be done more on the level of you can get new skills/spells once you have enough of certain stats. So you have 3 magic skills - Offensive, Defensive and Summoning, which determine how strong each spell of that category is. And the higher that skill is, the more different spells you can learn under that category. It still allows for very diverse, unique characters, without the limiting of just a few spells/skills throughout the whole game.
Some examples of skills/spells could be:
-The primary stats (Strength, Agility, Braveness, Intelligence, Wisdom)
-Each different weapon type (pistols, rifles, heavy weapons, etc) which increase accuracy/damage
-Lockpicking (unlock locked doors)
-Stealth (hide from sight)
-Perception (see better)
-Speed (move/attack/reload faster)
-Parrying (avoid being hit)
-Critical Hit (raises critical hit chance)
-Reloading (increase reload speed)
-Immunity (decrease magic attack damage)
-Regenerate (increase health recovery rate)
-Rest (increase endurance recovery rate)
-Meditate (increase magic recovery rate)
Just stuff kinda like that. I think you get the idea.
Sorry if that was confusing.