I'm going to be the dissenting voice here; I think Zilean's rework makes him extremely fun now, as long as you break the old habit of maxing your bombs, and max E>W>Q to become a ridiculous speeding/slowing ultra-rapid 1-Up carrying machine.
I also enjoy the stun mechanic because it allows me to cut off paths, which I do quite, quite often. Super quickly QWQ a spot with enemies running in that direction, and they either freeze to avoid it, or freeze because they stepped on it and got stunned.
HOWEVER, I agree that his bombs are too unreliable to land, and that he's in a bad place overall right now. Playing him in lane as support feels like there's absolutely no reason to play him. I was playing Zilean support earlier and a thresh hit me with two auto attacks for about 300 damage, likely due to his extra magic damage on some auto attacks. I realized that as Zilean, I would have had to have landed 1-2 bombs to match that damage, but at the cost of mana, and unreliability, and then being on a long cooldown, and also he's way squisher than thresh.
Furthermore, his passive feels useless since they nerfed the range.
But here's where the real issue lies. You have two skill paths to choose from as Zilean, realistically.
- You max your bomb in lane, so that you actually hurt the enemy with your poke instead of it being something thresh blocks with his lantern casually every ~8-10 seconds. So, okay, you have decently damaging but unreliable poke.
The problem is that you transition into being much worse mid-game because your slow is so much worse than it used to be, even maxing it second. So you poke decently in lane, but are slow and unhelpful after the laning phase.
OR:
- You max your Speed and then your Rewind. The result? Your laning phase is mega-shitty; you do nearly no damage, save for at level 1 perhaps. But you have a potent slow/speed up to set up ganks relatively easily, if the jungler decides to come. But more importantly, you're actually useful after the laning phase ends. You get to keep yourself super-rapid most of the time, running around, hard to catch, throwing wards and scouting bushes with bombs, etc. It's at this point that he can make huge plays happen just by using his speed/slow to assist a tanky or melee champion (usually his toplaner or jungler).
So either you have a mediocre laning phase, then become shitty, or you start off shitty, then become potentially REALLY helpful.
Obviously the 2nd option is better. And that's where you run into his major problem. If you want to be useful as Zilean, you have to take the level route that makes you horribly weak in lane. And what tends to dominate the support meta?
Champions that can make you instantly die if they land one ability at the right moment. 
AKA, champions with absurdly strong lane-presence just from their utility.
So, for example, Annie can max whatever she wants first and still be extremely useful in lane by landing a stun on the enemy. If Zilean wants to have any sort of presence like that in lane, he has to max his bombs, and even then, it's less reliable for damage and pretty much useless for actually stunning & killing the enemy. (You can get lucky and land a double bomb, and then you have nothing but auto attacks to hurt the stunned target. Morgana, for example, can pool beneath you. Annie has a burst rotation. Thresh can flay & follow up with enhanced autos. Blitz has the knockup and, at 6, the silence.)
You get the point. The way his kit is designed turned him from previously a reliable lane poker into now "You only get to have one of your abilities be useful; the bombs, or the speed/slow. Choose wisely."
That is the fundamentally broken part in my eyes. I really would like my bombs to be useful. But if I sacrifice even one point in my E/w, I'm sacrificing a huge part of my speed/slowing power, so I can't afford to make my bombs useful.
Oh, and one last thing. As mentioned before; the speed-cap/"diminishing returns" on your speed boost really, really sucks. It's up from 55% to 99% now - almost 2x as much of a bonus - but it certainly doesn't feel anywhere near 2x as strong. Only slightly stronger, maybe 15-20% more. Although it does feel quite potent on enemy champions now, that's counteracted by how short the duration is.
At 40% CDR and max level W and E, you still can't have your E on yourself permanently. The old Zilean could have himself sped up permanently and still speed up someone nearby a bit as well. Theoretically the gaps in your speed boost are "made up for" by the increased speed effectiveness, but it doesn't feel nearly as good, going in constant little bursts of speed instead of reaching that end-game fantasy of being permanently super-fast like he could be before.
Last but not least, the decrease from 7s to 5s on the ulti sounds like counterplay addition, but it became more of an issue of baiting your allies into killing themselves. They see the ulti, hesitate, then decide to go in and try to die with it. So either 1) they die with it and then get killed on the spot upon revival, which was already an issue before, or more pressingly; 2) they panic and run into the enemies and die a brief moment after your mark expires.
As a Zilean player, it's really disappointing how many times I've heard people sadly comment how the Zilean ult just barely ran out by the time they died. But the irony is, if they didn't have my ultimate on them, THEY MIGHT HAVE JUST RUN AWAY TO BEGIN WITH.
Is the impact of what I'm saying here being fully understood? Zilean's ulti, which is supposed to specifically save someone's life, now often kills your ally by baiting them just long enough into running by the enemies and getting killed after the mark expires.
So yeah, taking away the bomb's reliability, then nerfing his E range (which really, really sucks) to make sure the bombs stay unreliable, then also making his ulti sometimes kill your allies by reducing the mark duration - the addition of the stun really didn't compensate him enough.
There needs to be improvements. There really, really needs to be improvements. Starting with, in my opinion, increasing his E back to the old range. Following this, they need to make his W on precisely a low enough cooldown at rank 5 that at MAX CDR and MAX RANK IN E AND W, you can once again reach the end-game fantasy of keeping the speed boost of E applied to yourself PERMANENTLY.
This is probably the thing that made him the most fun before and the most devastating thing they removed from him. The ability to stay permanently sped once you finally met the right conditions later on in the game.
The maths are a little too wonky for myself, but essentially, with 40% CDR and W at max rank, you need to be able to pull your E off cooldown precisely every 2.5 seconds, which is just as long as the speed's duration. So you can permanently speed yourself (at the cost of constant mana drain) or you can alternate speeding yourself and an ally non-permanently.
I don't know what W cooldown would facilitate this - it seems that it would be 4.16666~ seconds, so that at 40% CDR it's at precisely 2.5 seconds between uses - but 4.16666~s cooldown is a little bit strange, so making his W a flat 4s cooldown at rank 5 would be IMMENSELY helpful on its own, both in terms of viability and in terms of FUN.
Because of these W and E improvements, he wouldn't need to have his bombs changed, because his kit would synergize better - with the return to the old range on his E, it would actually be used to land the bombs more easily now, which should be the whole point, instead of them lowering his E's range to purposely avoid that. With how squishy he is, you can't really get in E range to land your bombs now that the E range was nerfed. It needs these improvements.
After that, I'd increase the ulti's Mark duration to 6 seconds, maybe 7 like it originally was. 6 should be okay.
Last but not least; scrap the passive. Make it something you actually feel.
These are my long, drawn-out thoughts, and I'm sure you guys won't feel like reading it all, but thanks for reading whatever parts of it that you do.
I think I'll make my own thread on this.
Q 
Q 
Q ) Which you definitely are not!
received his rework the same time 
did. That's the only possible explanation.
I can relate...
