If you are looking for an MMO that has a more complex, and action ability usage tanking style, I would recommend Tera. Tanking in that game is a blast and requires you to activate your "block" in real time, or else you can get smashed by bosses. There is something uniquely exciting, and unforgiving when you know that if you fail to block an attack, you can get one shot, even as a tank!

The downside is that because the game is more challenging, player skill levels vary wildly. But I played it for 6 months and had a blast with it!