Nice movespeed, but the damage is really bad. The scaling is so low, that its barely enough to nudge out of MR damage
So most of the time it hits 96*-lower
So generally after it's bought (I see noobs first iteming it) I view it as more of a 2nd buy.
So around 200 ap. . this items kinda weak. Magic pen and Liche bane just outclass this item by so much that I don't know why it hasnt been buffed up or lowered in price.
IA9hRfpP5q2 votesLuden's 
ReshiKillim1 votesLuden's has a history of being a unholy terror, which is why it is in its current state. And it's generally best on siege/poke mages, which are both the types that don't want to get into autoattacking range. Luden's is sort-of a niche item outside the raw stats.
NikaLeetKila1 votesIt used to be 120 AP, with a 15% ap ratio. Now its 100ap with a 10% ratio and still costs the same. See where I'm getting at here?
If the item had 10% cooldown reduction and costed the same it would make sense. After the mage update no one uses this item at all so I don't know what you're getting item as a niche item, when all of the niche items beat it in raw stats also. (Hextech dealing 100-200 damage and 35% ap ratio, also giving health and a slow lol)
ReshiKillim1 votesXerath and Vel'koz get a lot out of it, though Xerath has always been the one who benefits most from Luden's.
And with Xerath or Vel'koz, you don't want to be close enough to the enemy to use the hextech actives on them. It doesn't need more stats, as it would make it too strong on champions that synergize with it.
It's a great item for siege mages, and it being too strong on siege mages was why it got nerfed in the first place, as they want to lay down damage from a long distance away while the hextech items are significantly better in close-mid range.