Before we discuss the specs, however, a quick note on gear: I'm gearing for grinding/questing in a mix of DPS and tanking gear. Basically, I'm going for shield block value as high as I can get it while keeping a good mix of offensive stats like crit, hit and expertise, and trying to do as much of the shield block as I can through high strength on gear. I still have a few pure SBV pieces like my Coren's Lucky Coin equipped, but in general the priority is strength/SBV, crit, hit/expertise. Since I'm still wearing a few high SBV tanking pieces (and some other drops that are just plain high in stam) my health isn't low for this strategy. At present in defensive stance I'm sitting at about 1700 AP, 950 SBV, 16.5% crit.
The spec I decided on I didn't actually choose until level 73, but we'll look at a level 70 version of it now. First, let's tick off the really big omissions of this spec: it lacks Anticipation, a solid talent that you wouldn't want to raid tank without. It's also missing Improved Bloodrage, which is one of my favorites, and both Improved Spell Reflection (awesome in a group) and Improved Disciplines. Finally, it lacks Vigilance, which is very nice for 5 man and raid tanking. It also lacks Safeguard, and maybe someday I'll care about that talent. I eagerly anticipate the impassioned defenses of Safeguard in the comments. I only wish I could share your fervor, but to my mind Safeguard lacks the one thing it would need to belong in the new prot tree, which is any good reason to take it at all.
Look for my upcoming book, I hate Safeguard, in bookstores soon.
Anyway, what does the spec have? Obviously I rocketed up the spec as fast as I could to get Shockwave, Damage Shield, Warbringer and Critical Block. The damage heart of the tree is the triad of Critical Block, Incite and Improved Revenge. Yes, Imp Revenge is worth taking, as it increases the damage of your revenges by 20% fully talented. You'll see a nice damage boost to your critical hits with Revenge, believe me, between all the strength you're packing and this talent. (Revenge gets a good deal of benefit from your AP now, after all.) Meanwhile, Shield Mastery raises your block value, Gag Order jacks up your Shield Slam damage by 10%, and Critical Block raises your Shield Slam crit chance by up to 15%. Incite raises Heroic Strike, Cleave and Thunder Clap critical hit chance by 15%. At this point, with a 16% critical hit chance, you're looking at 31% chance to crit with just about every ability you use while still sitting in defensive stance for the benefits of Improved Defensive Stance. A 100% chance to go enraged every time you block? Yes please. This gets even better once you get Enraged Regeneration. Pull 10 mobs, pop Shield Block, then use Enraged Regeneration and heal while they're beating themselves half to death on your armor and you are thunder clapping and shockwaving in their faces.
Now, you don't get ER until 75. So let's look at a level 75 version of the spec. Building on the previous version we now have ourselves Impale in the arms tree. Why did we want Impale? Because every time one of those various abilities we have talent boosted to above 30% citical hit chance actually crits, it will hit 20% harder. Shield Slamming for 2k on a crit? Now you're critical hit with shield slam is 2400. We spent five points up the arms tree, and now all those lovely critical hits we're doing, our cleaves and thunder claps and shield slams and revenges, they're all hitting 20% harder. Not to mention that we get Improved Charge, which we can use in combat thanks to Warbringer, and get more rage back from it.
You can absolutely, and easily, tank a five man instance with this spec: I've tanked up to Gundrak in it. (Technically I've tanked Gundrak with an extra point in it, since I was 76 when I did it.) Not much of an issue with rage, threat's solid, no complaints from the healers (I did throw on more pure tanking gear so my crit was lower, admittedly). While it's definitely lacking in some nice abilities for raid tanking, it puts out very, very nice threat via trhe damage potential of the spec.
The level 80 version of the spec is just the level 75 version with an extra 5% crit from Cruelty.This is where I'm heading now: in two levels I'll probably see if this is good enough for heroics or if I have to drop damage/threat abilities for more survivability. If I do I may go with this variant, which puts those five points into Anticipation instead. I could peel points from arms, too, but man I really don't want to lose Impale. I'm currently using the Glyph of Revenge and Glyph of Heroic Strike as my major glyphs, with the Glyph of Charge, Glyph of Bloodrage and Glyph of Thunder Clap as my minors. I may take the TC glyph out, I'm not really sure I need more range on that ability.
Next week we'll probably talk about arms leveling specs, because I owe arms some love, and it is a very solid spec right now.