It’s toolkit works the best in m+, but it’s good in raids too.
The rotation can be very good if you spec for it, and honestly, most specs have 4 or 5 main abilities that they use to do most of the damage. And that’s fine.
Overall id say that havoc is top tier in gameplay too. It’s not as good as outlaw rogue gameplay though, but outlaw rogue is pretty much unbeatable in that aspect.
Rogue at the moment is probably the best designed class overall, and it has the numbers to back it up too.
Now days if you play M+ build or so called AOE spec it is all about burst windows every 40 sec when Eye beam and Essence breaks goes of CD.
In real case scenario you have to adapt you rotation to what is happening around you and maybe hold a skill or 2 for next pack Like Eye Beam/Essence Break. Or if for example something dangerous soon will happen so you have to move out of melee range and so on. Most important i would say is that you try to do the burst rotation right if you play Momentum/Essence Break build.
Preferably turn around and vengeful retreat backwards through your target so you land in melee range but can be tricky to do so if you land out of range use Fel Blade or Felrush to get in range.
If you land within melee range you can fit 2 Anhilliations in the 4 second Essence Break window. If i remember right your haste had to be around +11% and most DH got less now days. But it is a good thing to think about if for example Bloodlust/Heroism is cast and you got the extra haste.
Here is rotation taken from icy veins so you get the idea of how it is to play DH now days.
Havoc has a lot of talents that link up with each other in a powerful way, usually having one pick having a powerful interaction with another elsewhere on the tier. Examples of this are Felblade paired with Demon Blades; Initiative, Unbound Chaos, and Momentum together; or finally Furious Throws, Accelerating Blade, and Soulrend. In many cases, the talents enable each other and should not be run alone.
In AoE when playing Soulrend and supporting talents it becomes a high priority with crazy DPS. Watch out and prioritise casting Throw Glaive to prevent it from getting overcapped/unused to optimize DPS.