I love the design of this card. 3 damage in 1 card is incredible, but part of what makes allies the best card type in the game is the ability to soak up a big attack with their last point of health. This makes for an interesting decision both in how we choose our allies during deckbuilding and in gameplay. You are more likely to use Last Stand if your ally is already a huge beater and you would have wanted to attack with it anyway. I personally look forward to using this with Goliath.
Conclusion: Last Stand makes it into the sweet spot of card design that is neither unplayable nor a staple but should always be in consideration based on your strategy and supporting cards.