'Ridiculous' is a great adjective to put in the title of your game: perhaps the best videogame adjective since Gratuitous Space Battles*. In an App Store stuffed with desperation, it's charming for someone to pick a name that doesn't reek of SEO.
This isn't a fishing game, by the way. At least, I don't think it is. Ridiculous Fishing wears borrowed robes, like Shadow of the Colossus, the PS2 RPG that had a lot more in common with contemporary puzzlers. SotC was a wonderful game, possibly helped by that generic sleight of hand; I played RPGs almost exclusively in those days, and the game's episodic, grind-free take on the genre was a lovely surprise.
Ridiculous Fishing doesn't have much to do with fishing, I don't think, nor with the fishing sim genre as it's generally understood. There's no waiting around, hoping for a bite. You don't roam a lake or sea in a rowboat, searching for the best spot. There's no test of patience or endurance. You just speed a hook down into the darkness and navigate madly between the shoals, get as deep as you can then repeat the trick in reverse to bring your catch to the surface. It's actually more like a side-scrolling bullet-hell shooter – turned on its end, admittedly – than any fishing game I've ever seen.
I think the best thing about Ridiculous Fishing is that reversal, which doesn't just apply to the direction of travel but to the mechanism too. On the way down you're avoiding fish; as soon as you hit one (power-ups notwithstanding) that's the end of your dive, the hook clogs or whatever and you start heading back up. But then the purpose switches and you have to pick up as many fish as you can on your apparently Tardis-like hook.
* I haven't played Gratuitous Space Battles. I don't like to namedrop games I haven't played, but I thought I would make an exception here since it's the title itself that I love. Like judging a book by its cover would be fine so long as you confine your comments to "The cover is quite nice."