I still play morde a fair bit, but nowhere as much as I did in season 1. I've played him when he was an early game monster with no late game, I've played him when building ad was a legitimate option, and I've played him all throughout the latest slew of changes. I feel pretty confident in my own opinion when I say he can still hang with any other champion, but he has to work so much harder for every little thing that it's just very stressful to play him. Every time I play morde and I see malzahar in the enemy lane I smash my head on the desk because I'm in for perhaps the most stressful 20 minutes imaginable. You always had to really outmicro the enemy to make good trades in harass, especially ranged enemies. With the shield nerfs, most harass opportunities are simply off the table now, because very few champions can't give harder than morde's e + the shield it generates now - of course the health cost of it. In order to actually survive laning with morde, you have to play so incredibly carefully, managing your health, constantly aware of your position, the enemy position, the enemy's ability casts, and most of all the minion flow. Does the enemy need to keep track of all that to fight morde? Not really. Wait until he's used siphon and then harass him for free. If he doesn't use siphon? hit him anyway since he has no shield. If he siphon's you after, you came out of it better, guaranteed. That's basically it.
I'm fine with counter play to morde, I really am, but the best counter play has always been and probably always will be buying mr, and having the jungle ganks in laning. My big beef with the nerfs is that they just made life ****ty for morde players, without actually changing any of the dynamics that had people crying about him before. If he gets a leg up on you, he can push all he wants and there's nothing you can do about it. If you get to late game with him, morde is still the same as ever. He's still the big metal steamroller. He just has to get past an unbelievably frustrating early game to get there. He's got a power curve like a hard carry, but unlike dota, the game isn't set up for hard carries. So instead of a high risk high reward system, it all comes down to what the enemy does. There's the inevitability of morde powering up eventually, but there's also an inability for him to speed up the process in any way. He's not a ganker, and he can't hunt people, so he's just left sitting on his heels and hoping the enemy team lets him get away with things he shouldn't.
Suggested changes? I think Morde suffers from inconsistent design decisions more than anything else. He's had everything messed with for different reasons and I don't get the impression the balance team actually knows what they want him to be. He's somewhere between an ap carry and a tanky dps. He scales like a carry, but his abilities all say melee damage soak, but he doesn't have any of the mobility or cc of either, and neither of those types have the same early game weakness he does.
So my suggestion? If he's supposed to be an ap carry, make it so that creeping death can be put on an enemy. Make it reduce their armor and mr by an equivalent amount that it would buff an ally, and make it slow them.
If he's supposed to be a melee dps? Make creeping death give a move speed buff. Not having cc is somewhat a part of who he is, but he has serious trouble staying on people since all of his abilities besides creeping death makes him stop moving to use, and he needs the mobility to make use of half his kit.