i intended to make a necromancer in morrowind, i'd do what i wanted, but before long, my character just morphed into a hero before my eyes, and i couldnt bare to let even one life be snuffed out, even when it came to enemies, i'd only kill if absolutely necessary, my character became what i liked to call a "blade-mage" ...a strong mage with a wide array of magic, but also being a master at long swords.
i tried this again in oblivion, thinking i'd just make a necromancer, even more so since we were capable of stealing NPC souls... but, of course... he ended up becoming a hero, another blade-mage, actually he became a student of my previous character, and he was left in charge.
so... i think skyrim's way of doing things might work out, because i wont need to worry about making false assumptions about my characters' destiny, and they can simply use what they will use and still level up from it.
you can still make up rules for yourself, just make a list on paper of what your character will be and what skills they'll use, if all you needed were imaginary rules, make up your own, it cant be much different than choosing them in-game, because in reality, even choosing the rules you'd go by in-game still doesnt stop you from using whatever skill you wanted.