Since patch 3.0.2 went live, the functionality of Deep Wounds changed considerably making it significantly more powerful.
Previously, Deep Wounds lasted 12 seconds, ticking every 3 seconds. Any crits reset the duration and overwrote the previous buff entirely. This meant that the actual effect of the talent was far less than would be expected. Any crit within 12 seconds of the previous crit would diminish the effect, and crits in under 3 seconds would prevent it from working entirely.
Presently, Deep Wounds has been changed to a 6 second debuff, ticking every second. New crits reset the duration of the debuff, but add the damage to the debuff rather than overwriting it. This allows Deep Wounds to essentially act as a damage buffer, ensuring that the full Deep Wounds proc damage will occur with every crit. Main hand and special ability crits apply Deep Wounds damage based on the percentage of MH weapon damage formula. Off hand crits apply Deep Wounds damage based on a percentage of OH weapon damage.
Example) Your average MH weapon damage is 100, meaning Deep Wounds will deal 48 damage with 3 ranks per application.
0 seconds: You land a critical attack. The DW debuff is added with a total of 48 damage and 6 seconds remaining
1 second: Deep Wounds deals 8 damage.
2 seconds: Deep Wounds deals 8 damage.
3 seconds: Deep Wounds deals 8 damage. You land another critical attack. DW duration is reset to 6 seconds, and the new damage is the remaining damage plus 48, 48-(3*8)+48 = 72.
4 seconds: Deep Wounds deals 12 damage.
5 seconds: Deep Wounds deals 12 damage.
6 seconds: Deep Wounds deals 12 damage.
7 seconds: Deep Wounds deals 12 damage.
8 seconds: Deep Wounds deals 12 damage. You land another critical attack. DW duration is reset to 6 seconds, and the new damage is the remaining damage plus 48, 72-(5*12)+48 = 60.
9-15 seconds: Deep Wounds deals 10 damage.
This functionality is identical to Ignite's.
A Critical strike, dealt with ranged weapon will also trigger Deep Wounds, but deals still 1/3 of your Melee Weapon Damage, not the ranged weapon. (USeful for killing runners with Thrown weapons.)