The best leveling and character building system i have encountered so far was that of Guildwas, i managed to burn arround 4200 hours in that game, had a guild with 25 active players we were a mostly pure PVE guild with but lots of fun in the later not so serrious PvP areas from the first addon.
The System allowed me to freely combine at any given time any attribute and skillpoints you had at any level your had at the time. Later they included a build load/save function which then made me collect all the builds of all my 10 characters which in the end i had a collection of arround 140 builds. For any type of situation, any type of foes and any type of team combos needed i had my build for it
i loved to have that collection and i was able to tell you all about the the skills in those builds, i followed any patch and how those skills were changed and i changed first hand my builds acordingly if needed.
If not for the option to flexible recombine my attributes and skills i would have been out of the game after perhaps 500-700 hours if not for the loading of builts i would have been perhaps out of that game after 1400 hours. Giving the player the abilities to complettly customize his char over and over again is a huge turn on