I'm planning on buying mordekaiser, how is he currently?

Everything is his weak spot. He is in a pretty terrible place. Do not recomend at the moment

He's not in the best place. He's kind of gimicky at the moment and those gimicks aren't really working for him. All of his critical itemization is too expensive, and he can't function in the jungle to take any shortcuts to power spikes. The intention was essentially that landing his Q would be a oneshot, but they nerfed the damage on it, so, while it's strong, it's not insanely over powered and the rest of his kit (ult aside) is fairly underwhelming.

In the process of the rework, the destroyed how effective he is when fighting alone, weakened his primary means of building shield as well as his secondary and reduced the damage on his ult somewhat. It's also really important that you build a means of slowing other champions into his kit as well as a phage to keep him in range once he lands first q. However it times out really quickly so it's easy to take the first two hits and then use a movement skill to avoid the third unless he flashes.

He was meant to feel as though being stuck in his range is a death sentence but it's rare that you'll be forced into that situation, and it's somewhat true, but with the nerfs he takes too long to get up to speed and requires the presence of a second champion to get the most damage out of his kit.

He can still dominate bot under the right conditions, mostly getting to pick last, so it's not clear the intention is morde bot. After the ADC rework, most of them run circles around him, getting dragon is way too critical to his success. Buy him right now, if you like the idea and you're willing to put in a ton of work and have a dedicated support lined up. However if none of those are doable for you, hold off until either his kit is altered again or his itemization is changed.

Hes being played in a solo lane again, and if im not mistaken, they i THINK are buffing his W on PBE.