Hey /tg/, let's talk about tactical combat systems and roles. D&D 4e does tactical combat very well, but I wonder if certain roles and mechanics could be done differently.

First of all, I wonder if there's a better way to do a "tank" than the Mark mechanic in 4e. For those who don't know, defender roles in 4e can apply Marks to enemies which causes them to take accuracy penalties for attacks that don't target the defender, and there's often a punishment mechanic too.

This is great for an aggressive defending style, but I feel like it's not a good way to represent someone who's just a big wall who stands in the way and blocks hits. What systems do a better job of the "unbreakable shield" sort of defender?

Second, attacks of opportunity make positioning important, but they can really slow down combat. What are the best or most clever ways you've seen systems make positioning important without slowing down combat to a slog?

I'm also just wondering in general whether there are good ways to break out of the mold of tank/defender, healer/support, damage dealer, crowd control as combat roles. I haven't seen it much in systems which do attempt to codify combat roles.