Luna's a pretty decent hero. If she gets farmed up, she becomes a very hard to stop agility carry. The fact that she has a 300 damage ministun nuke which also affects how much damage her ult gets, along with the passives that A) Increase her base damage by a percentage (and stacks with Drow's) and B) Allows her to quickly take down creep waves (as well as remain useful in multi-shotting team fights if they get too close to each other; never underestimate Moon Glaives) she does end up fairly well rounded.
Never build her as a caster though. That's just dumb, squandering the potential of her to carry hard over a 140 second cooldown.
And speaking of multi-shotting, I can't wait until they add Gorgon back in. She's basically the epitome of tanky carry, with a mana shield that reduces damage by 50% (and allows for 2 damage per point of mana), an ability that steals mana (and can chain to multiple units), a split shot allowing her to shoot 5 (which is more than I remember it being, to be honest, but I also remember when her ultimate was simply an awesome Purge rather than a Purge that casts on units looking at her) arrows at 75% damage each, with your main attack still applying Skadi... Yeah, she was nice, if you build her right. Skadi + Linkens + (Insert generic agility carry items here. I think Satanic was good on her too, since it stacks with Skadi on ranged heroes, but I forget how it interacted with her Split Shot).