20 could be the level limit, I'm not sure. That was the limit in the Preview. You started at level 15 and capped at 20. I don't know if that stays in the retail but according to the developers on the VN boards, it hasn't been decided. It'll be a low number in that range, though.
Since the focus of the game is to have balance in both PVP and missions, rather than having a levelling race, having a low level cap really works out. The game becomes more about skill and fun rather than levelling up as you would in an MMORPG.
Surlent is right, too. It doesn't matter if the game has time sinks. Diablo 2 and Dungeon Siege both had time sinks in the form of equipment, upgrades (runes), and new skills. But guess what? Beyond buying the games an their expansions (which were entirely optional), they were both free to play. Just look at how vibrant the Diablo 2 non-expansion pack community is. Instead of trading in high level runes and elite items as Expansion players do, they spend most of their time trading really good Rares. Those are time sinks. Do they detract from the game?
Nope.