EDIT: Also, (actual LoL speak), Ziggs seems kinda eh. I have to see him fed before having an opinion.
Even if you get fed (which would require stealing assists in side lanes, or having a terrible mid lane person?), your ult will do like...1000 damage mid-to-late game. Even with sorc shoes and void staff, 1000 damage is not much given enemies stacking health and magic resist, and it's surprisingly hard to hit enemy champions with it. If you drop it on say, Poppy, and she's close to you (say a river's width distance away), even if the middle is dropped on her she can run past the edge of the bomb before it lands. Or at least, that's what apparently happened yesterday when I was playing Ziggs and Poppy was running.
It makes it even more hard to hit when you consider that its angle/flight time varies depending on how far away you are, so you can't just try to time it like Pantheon's ult.
Lastly, as I mentioned earlier, Ziggs has no silence or stun, and you will be LUCKY if you can get decent damage by dropping the minefield into enemy champions in a teamfight without getting murdered by them. The satchel has a huge cooldown and you would be even luckier to do much enemy damage with that.
As a result you're left with a potential minefield slow, a low-cooldown Q that takes practice to aim (you can launch it in a straight line at someone and miss, unlike the vast majority of skillshot Q's?), and super high mana costs if you try to use low-cooldown Q often. Oh and your 90-second cooldown ult that's great for teamfights but doesn't have lockdown power like Malzahar or Annie, and your passive which makes your autoattack more powerful...though getting in autoattack range with mages tends to be bad news. =P
Anyone tried Satchel-Turret pwning with Ziggs in a way that you throw the satchel behind the enemy that's attacking your tower and then blow it so he has to stay in turret range longer? Kinda like Blitzcrank juking with the hookshot->knock up and what not. Maybe minefielding his escape route too. Just wondering if it works, haven't tried Ziggs.
Pondering over my next champ purchase, but Ziggs might not be the first choice.
The satchel knock distance is very small as far as I'm aware. You CAN jump over walls into Baron with it, but it's hard to even do that since it has to be placed in just the right spot. Maybe if you hit it just right and an enemy is obligingly in the right spot, you could knock them the same distance that it takes to jump into Baron.
My experience has been that if you use satchels and minefields to try to block people's escape, they will instead cruise forwards and nuke you (since you now have no escape besides flash, and no ability besides Q, lol).
He's pretty fun and silly, but definitely wait until the free week to see if you want to buy him.