Shockwave has its limitations, of course. The fact that it is a frontal cone and not a true AoE spell means that the warrior using it for threat while tanking must take care to position himself properly to hit everyone he wants, which of course takes time and means you may be trying to angle away from CC and such. It's not a huge impediment, but it is something to consider. More problematic for pure threat is that the stun component will inhibit rage generation and this is a downside for a rage-based tank like a warrior.
These aren't huge liabilities in my opinion but they're there and need to be considered. With those aside, though, it's a nice spike of damage to multiple mobs every 20 seconds, and for that reason alone it's worth adding to any tanking rotation.
For soloing, however, it's very, very nice. You can have a group of five or six mobs hitting you and between this ability, Damage Shield and Enraged Regeneration (expect to see them get their own Skill Mastery spotlights soon) you can very easily whittle them down while minimizing your own incoming damage. Shockwave is one of those talents that could probably use some tweaking upwards in damage or a reduction in the cooldown (15 seconds would be plenty between Shockwaves in my opinion) but it's a solid, workhorse ability that helps break up a warrior's rotations and is useable in and out of instances.
And of course a 4 second cone stun has implications for protection spec in PvP. But I'll talk more about then when I discuss Warbringer.