I do find myself prioritizing DS almost over any other attack. The survivability and damage combo just makes it too tempting. What bothers me is I am not often compelled to use heart strike unless I have nothing else to do or need to refresh my 6% damage debuff. (talking single target) But all in all I feel comfortable where DKs are.

Maintain two diseases to reduce physical damage and attack speed, maintain self damage reduction buff, DS for self heals and threats with runestrikes at higher than 50% runic power. In a troll dungeon I will output 15k dps on a boss ( but thats with a 15% roullet bonus, so in reality its more like 12k ). That's 5 choices on my single target attacks alone.

Now to throw into the mix all our cooldowns: Runetap/Bloodtap for health and rune management.; Ice Bound Fortitude our big cooldown, Vampiric blood our smaller cooldown, maintain bone shield another smaller cooldown, anti magic shields for magic burst, and finally lichborne for that big self heal.

That's 6 more choices and we are not even getting into trinkets ( I use two cooldown trinkets mind you ).

So at this time I sit with a dozen choices to make at every global cooldown as a DK tank and I really enjoy it. I have a bear tank and paladin tank and I don't actually feel I have any choices. Yes, DK is a bit more complicated, but its a lot of fun for me.

While I like the idea of tying different abilities we already have quite a few, though I would like to see Blade Barrier proc whenever HS is used.

Here is a recap of our abilities that are tied to survival for those who don't know DKs
Icy Touch = melee slow debuff 20%
Plague Strike = physical damage debuff 10%
Heart Strike x2 (or any 2 blood runes) = 6% damage reduction buff
Death Strike = Self heal and a physical shield
Rune Strike = possibly refreshing other runes.

Death knight is in a good place right now, and well designed in my opinion.