Thought about this question after reading the CRPG Addict's blog and the guy considers leveling up an absolute core element of the genre, to the point that he considers a game with no char creation and a simplistic leveling system more of an RPG than a game with complex char creation but no leveling.
So let's set this straight with a Codex poll.
Let's take a look at two hypothetical games, both at opposite extremes. One of them has a complex and engaging character creation system, but no levelups. The other has no character creation and no customization, but it has leveling, and a lot of it.
In game A, you can choose everything about your character. Sex and appearance, skills, perks, etc. You can pick between a male or female character, customize his/her appearance, and you get 1000 points to invest into various stats and skills in a flexible classless system. There's a couple of Fallout-style perks you can buy with your points, too. You can play a female assassin who focuses on stealth, backstabs, and seduction. Or you can play a tough barbarian with high strength and high weapon skills but the charisma of a dead toad. Or you can play a wizard fully focused on intelligence and spellcasting, but zero points in any physical weapon skills. Or you can go for the jack of all trades.
But once you have created your character, that's it. Nothing in the game gives XP, you will never level up. You create your character and you're stuck with him/her.
In game B, there is no character creation. You play a male jack of all trades with 10 points in every stat and 1 point in every skill. You can't even customize his appearance, you gotta accept the ugly mug the devs chose for him. But there's a ton of leveling up to be done. Every action gives XP. Kill an enemy? XP. Pick a lock? XP. Finish a quest? XP. Talk to an NPC and find out a new piece of information? XP.
But whenever you level up, your character gets +1 in every stat and +1 in every skill, and that's it. You don't get to allocate any points as you see fit, the game just raises ALL your attributes by one on each level up. There is zero customization. You can't specialize into a fighter, thief, or mage, you are always gonna be a jack of all trades. There is no level cap, though, so you can keep leveling infinitely as long as you gather more XP.
Which of these is more of an RPG? Game A or game B?
The correct answer is, of course, "game A". This is not an opinion poll, it's a retard test.