Well I'm definitely not a favor of the WoW style ilvl approach. The constant carrot-on-a-stick gear mentality that we're always reaching for another 10 item levels. Achievements are kind of like a PVE Level though (granted PVP is involved in those) but things that show progression over gear do exist in the game. The way achievements are is that well, it shows how many dungeons you've cleared, how many raids you've done (to a point), how much crafting you do, leveling you do, etc.