A samurai or a knight don't level up in certain point of their life, what i mean is, after they going into war or doing mission, they are not suddenly receiving message "You have been level up! Choose your skill now" or "you must sleep in order to learn new skill" or in anyway to show that they have been level up.
So, how about a game that have no level up at all? Such as in TES, just remove the level up. The character may learn something new, learn combat skills/combat moves, learn new spells, learn to do this and that, but there is no level up. (In fact in Oblivion, one can stay at level 1 to the end but still have fun learning new spells and combat moves)
One will question about difficulties and balancing, i see no problem, in fact level up system bring problems and imbalanced game. It will be debated over and over and there will be thousands of mods that try to fix it.
The difficulty of the game can be set up with the excellent AI. For example, a trash mob do not have high AI than a boss type. Most of game system will make a boss that have 4 million health points, that make the boss is the boss, but this boss is static and robotic. there is no challenge other than reducing the 4 million health points to zero. With a good AI, 10 health points boss can give a challenge and hard to kill.
You see, a leader of a mafia gang is just a human but what make him a boss? It is his intelligent and his skill. A leader of a group become a leader because of they are not simple people.
Another example, in martial art sparring, both who fight are the same, but the difference between the two are the skill, intelligent, and many other factors. An opponent is hard to beat not because of he/she have 4 million health, but his/her skill in martial art.
It add realism in the game.
We don't level up in our life but we learn something new everyday, only how well we use what we have learned.