Inkzooka's a good special, not my favorite, but it's good.
Inkzooka shoots really tall inknados which make it good for splatting elevated snipers that you can't easily reach otherwise, it goes a pretty long distance so it probably reaches farther than your weapon normally does (unless it's the Squiffer; one of those has this, right?), the inknados move fairly quickly so enemies probably won't avoid it unless they see it coming from close to its maximum distance, and it splats in one hit, always, so you can't escape it like an Inkstrike or Killer Wail (Wail's escapable, right? It takes a couple of hits to splat, so I assume you can).
The big problems with this are that the inknados are fairly thin, not thin like individual bullets but not wide like a Roller swing, so you have to be somewhat precise, and it doesn't fire that quickly, so you won't get that many shots before it runs out (Special Duration Ups can mitigate this, but only so much), and it pushes you back a bit with each shot, which can push you over ledges or just out of range (you can get back in range, but that takes time you could be using to shoot more), and it doesn't shoot downward all that well, so it's not useful when you're shooting from an elevated position (not useless, but not as good as being on the same level as your targets, or even below them).
It's great for splattering enemies hiding in elevated areas (though not behind cover) and dealing with enemies your weapon can't normally reach (again, except maybe the Squiffer, if it has that).
Overall, it's alright. I prefer the Bubbler and Kraken (invincibility is nice), Inkstrikes too sometimes (hitting anything from anywhere is nice), but Inkzookas are pretty good to have too.