4 days remaining! Half a week left, and our long long wait will be over - at least, until we start clamoring for CivVI.
Tonight's UU is the Russian
Cossack, another veteran of past games. These famous border peoples are historically irrepressible and known for their martial prowess; thus, in Civ5, they get a
bonus against wounded units.
This is a tough ability to assess, since once again, it relies on how you use it. The obvious use is to pair your Cossacks with ranged attackers (Cannon and leftover Crossbowmen) and bombard, but in doing so you lose out on the Cossack's mobility. Of course, with the sheer power of this combination, you might not miss it.

Alternatively, if you prefer using your cavalry as flankers, you can use this UU brilliantly: take a front that's damaged and smash through with Cossacks. As a detachment for pillaging/intercepting, this bonus is less impressive. It's certainly useful - extra damage on the second attack never hurt - but not enough to merit special attention. Furthermore, the specific bonus against wounded units is unknown; not even the manual discusses it, so I can't say much certain about its usefulness. I suspect this is a unit that may be wonderful, or merely decent, but will require some field testing to see.