Even after the W nerf last patch he just seems really strong to me. You can't go double ramping items anymore but you don't need to if you aren't crazy with E. RoA-Rylais- NLR items as appropriate. (Rylais makes landing skittles a LOT easier and the W nerf easier to bear).
AyRe CoNteMpT2 votesyeah he has been one of the strongest 5 midlaners for the past 2 years and he still is
Erockandroll1 votesIn the past, I went with the double ramping items, in certain game modes that lacked a lot of CSing. (These were usually the featured gamemodes like Ascension or TT Hexakill) The Philosophy behind that was, If I can't scale off Minion farm, I'll scale off time.
This begs the question, if your not going double stacking, Are you going Tear, or RoA? RoA might still be good, given the tanky stats it gives you, though it does not have much in regen. (And I think a lot of Karthus builds require two mana items)
Regardless, Crystal scepter is a good option, especially if you are not going RoA. It does make up for the loss of HP from not taking RoA. And the Slow does help chase down the enemy.
Posui Gart1 votesRoA, Seraph and Rabadon are 3 of 4 AP items that have >100 AP. And RoA increases Seraph's AP because of its mana, resulting in something like 160 AP from Seraph. I usually get tear-RoA-Rylai-Seraph and later just finish it with Rabadon and Zhonyas/Void. Still has problems early against any assassin that is not dash-based, but lately in teamfights you have 
and 
for HP, 
and 
for shield, and when they finally finish you-a passive on top of it, with 800 dmg Qs flying around every second, 300+ DPS E around you and ult for 1100+ dmg in the end
Xenomancers1 votesWhat about 
? No tanky stats but the item pays for iteself and assists laning.
