Zilean, as far as i've experienced, is a champion who mostly win the game for his team if played right. A good 30 Zilean player can totaly domintate whole enemy team, and at the same time help his team to surive.

It should not be possible to have his ultimate up so often imo, it can be abused to create an imortal team;
Played a game today against Zilean, Alistart, Judicator, Gunner and Teemo, seriosuly was imposible to kill anyone except of Teemo and Gunner. This was much thanks to Zileans ulti and slow/haste.

Early-game, Zilean is an excellent harasser. Because his bombs are his only offensive spell, they have good scaling, which means he can do good damage with very low contact time. If you're jumping in & out and trading single spells, zilean tends to do well.

Time Warp is one of the best utility spells in the game. Used well in a team scenario, it can make or break ganks, in both directions. It's a very good teamwork skill as well, you can help allies escape, or you can speed up your team to help catch runners. Warp-Speed Rammusball is a great way to initiate on your terms, or catch multiple runners, plus it's just funny to see.

His Ultimate can get ridiculous, but it's not great when you first get it. The mana cost is prohibitive, and you can't spam recall yet for perma-rez. Late game you can cast it twice per battle, which is excessive for a cooldown nominally in the two-minute range.

The important thing about playing Zilean, is that he changes what sort of character he is at different phases of the game. Early game he's either an excellent harasser or an excellent laner (because Time Bomb is AoE too). Mid-game he's mostly utility, his bombs do decent damage but his speed/slow means that your team gets out alive and theirs not so much. Late-game he's practically a carry, because his scaling goes into full swing with 2-second recall and 1.1*AP on time bomb.

Bombs need to have a short range because they stick on a hero even if they run back they can't get away from taking the dmg themselves.

His ulti needs tweaking Like possibly a debuff it puts up that just disables it to be put up on a hero for a certain period of time. Heroes that have guardian angel with a Zilean on the team are just unstoppable.Specificly Any tank, Jax,Warwick, or even a well played Yi.

Also just a question but has the recall rank 5 recalling itself been fixed yet or does it still occur?

Personally, I think his speed boost time is spot on, but the slow time on Time Warp needs to be toned down a little. Seven seconds is a heck of a long time. I think this will give more of a risk/reward, whether to get a longer effect out of boosting a teammate into battle or slowing an opponent to get your whole team onto them. If you're running, you're never getting out of a 7 second slow unless you have boost, not to mention chaining 2 together.

I think Zilean is excellently made except for his cooldown-reduction spell. The fact that it procs itself makes all of his abilities have outrageously low cooldown times. A 20 second cooldown on his ult (the lowest it goes?) is simply too powerful. Making his cooldown-reduction spell not proc itself would go a long way to balancing him.

btw, it isnt just rank 5 recall that works this way; all ranks reduce their own cooldown by 10 seconds. It is just most noticeable at rank 5. If you have max CD reduction and spam recall on cooldown, the ult is about 25 seconds cooldown, at the expense of a very significant amount of extra mana. This is long enough that it will almost never be able to be used twice in a fight.

In general I find that zilean is a great champion all throughout the game, but isn't quite game breaking. His revive and bombs are both very strong, but the speed of battles coupled with his small bomb range and squishiness make him relatively balanced.

Zilean is decent early game, but late game he is one of the best champions in the game! His time bomb plus slows plus moe time bombs is such a great combo! Plus his ult keep him and allies alive! Recall has a bit of a balence problem (from what I've heard it Recalls itself, altough I've never noticed it)! Hes definutly one of my favorite champions!! Hes alot of fun and has a very unique concept!
my thanks go out to whoever designed him

With CD runes and a few CD items, ie getting to the 40% max, his ult CD is 11 seconds, with a duration of 15 seconds.