I think D&D is as strict as @BESW says, but that's what we (me at the very least) like about it? We're playing a game with set rules, that yes, has some wiggle room for interpretation, but a the end of the day what you can do is written somewhere, be it your character sheet or the handbooks. You can do original things, you can reflavor things, but at the end of the day you are playing with what you have.
I have played other games with more abstract limitations, wich I also like, but they both scratch different itches.