Why do you think he's a bad jungler?
- Easy clearing of camps. No AoE for super fast clearing, but W + Q = sustain + decently fast clearing.
- LVL 6 ult easily the best sure fire gank in the game. Probably the best or tied with Nocturne
- Not strong early; GDLK LVL 6; very strong late game.
- Ult = great initiation; especially for solo-queue where teams have players that constantly get caught out of position.
I don't get what makes him a bad jungler. He's literally like the Grandfather of Jungling with Nunu.
His clearspeed is bad, you're looking at around 4 minutes before you can actually do something even with perfect runes/masteries. This wouldn't be as much of a problem, but he doesn't really get faster on subsequent clears. This also makes him easily counterjungled.
He can barely gank till level 6, at which point there's a significant time for the enemy jungler to already make you lanes snowball.
He's near impossible to kill in his jungle, but he can't really kill enemies in his jungle either, even with ult without support (unless they're jungling somebody really squishy, but they're probably not counterjungling), combined with his slow initial and subsequent clears, this makes him incredibly easy to counterjungle, slowing down him reaching level 6 immensely. Even champs that wouldn't normally counterjungle will probably do it against a warwick.
Now let's look at his good points:
Fanstastic lategame
Near total item independance
Insane level 6 ganks
That's what it comes down to, are the level 6 ganks worth the total lack of control of your jungle and having really no way to stop lanes from snowballing until level 6? Especially since it's very likely that you're be getting to level 6 very late, even if you didn't get counterjungled.
Yes you can sort of gank with red and your ms steriod, but that requires them to be under 50 health and red buff isn't a powerful slow, especially since you don't bring much damage. Also, it ties into your whole "easily counterjungled problem".
I dunno I can't think of any comps where he'd actually be a good choice versus like 5 or 6 other junglers except maybe a true stall comp.