Well, where to begin...
For spec you have some very odd choices in talents. Specifically:
Annihilation? ScS is your FU move, not Oblit and 3% more crit on that is a meager buff for unholy.
Unholy Command, On a Pale Horse, Gargoyle, Master of Ghouls, Night of the Dead, and Wandering Plague are all standouts. Unholy Command is a talent I personally am not fond of since I aim by philosophy not to be taunting on CD. On a Pale Horse is nice for running around, farming, and for pvp, even the fear duration reduction is virtually application-less in raids. Gargoyle does plenty of damage, sure, but it does zero threat. Take it if you have an extra talent point and you want to boost your dps, otherwise, it's a waste as a tank with the talents that can benefit your tanking out there. Master of Ghouls aka Perma-ghoul is a fine talent for improving Ghoul efficiency, but as a tank it's pretty meager or pointless. Your ghoul gives you zero threat, and it's enough work to be on top of your tanking let alone to direct your ghoul at the same time. Night of the Dead is another ghoul buffing talent, see my previous sentence. Wandering Plague is a great fun talent, and it's really cool for aoe damage, but for one striking flaw for Unholy Tanks: our crit rating is miserable. I've tried it out because I really want it to be good, but it procs very infrequently so it makes it three points easily spent better elsewhere.
What's missing? I'll run through some again, Vicious Strikes, Impurity, Rage of Rivendare, and Bladed Armor are major items. Cases can be made for Necrosis, Blood caked Blades, and Desecration, though those are more often a personal choice. Vicious Strikes is worth more crit chance on ScS than Annihilation, and it comes with an increase in crit damage. Impurity buffs up several of the effects that would be major constituents of your threat, particularly UB and DnD for aoe threat, though several others as well. Rage of Rivendare is way too powerful not to have as deep Unholy. It is 10% increased damage (aka threat), and 5 expertise, that's expertise not just rating, is major threat and survival value. Be aware expertise up until you have 26 on your sheet is worth double the hit chance improvement of hit rating for all your melee abilities. Bladed Armor is massive. I can't undersell this, depending on your gear Bladed Armor will give you anywhere from 500-1000 AP as a tank!!
Spec aside, your gear looks quite solid, but for one major detail: expertise! You have 5 expertise which is worth 1.25% dodge and parry neglect, but raid bosses have a 6.4% dodge chance and upwards of 12-14% chance to parry. That will significantly hurt your ScS, PS, and BS damage, not to mention your melee. Those 4 combined for me represents about 40% or so of my total damage depending on how many things I'm aoeing.
You could get a little more avoidance value out of it if you swapped your parry/stam gems for dodge/stam gems, but I'd expect that is a very small detail, and it should have a pretty small impact on threat.
Other than that your rotation sounds fine, it's just a matter of hard work and effective use of runes, and again that's not something that should be developing unless you're getting lazy. =)