This skill is considered as one of the best in the game. The 10 second invulnerability period, combined with increase stats is more than enough to always kill whoever killed you in the first place. With this skill, you never die alone.
This skill can be exploited in fortress mode. The game type requires the destruction of fortresses. Since Last Stand makes you invulnerable, it is literally impossible to stop you from destroying fortresses, albeit at the cost of lives.