What I mean is, it's not creative, it's not original, and it gets boring really fast. Because it's extremely repetitive (even when it changes things up, I know what you mean, but the basic idea is still the same).
What I'm essentially criticising is that it's a brute force method of game design, it's not imaginative, it's not elegant in any way (whereas Splatoon is elegant in every possible way). It has no class. It's like b-movies.
It's like taking a hammer and hitting the ground with it for hours. It's dull. At least for me. I'm not saying others can't have fun with that, that's totally fine. If it's fun for you, it's fun for you. Fun is a very subjective phenomenon. :)
But in my opinion that's a game design method that's beneath Nintendo and especially, beneath Splatoon, because Splatoon is so artful and anything but dull. So if they want to add modes to Splatoon, they should be on the same creative level as the other modes.
Just imagine the thought process behind building a horde mode:
"Ok, so we let the player fight 10 enemies in the first wave... and when he gets past that, we hit him with *drumroll* 20 enemies! And after that, we give him 50 enemies... and then we give him 50 enemies with more powerful attacks. And then we give him 50 enemies with more powerful attacks and also the player has less hearts. And then, surprise surprise, we give him 50 enemies that are more powerful, while the player has not only less hearts, but only one life. And so on."
You get what I mean? That's not creative. Anyone can come up with that. Even if you mix things up a bit by adding new elements. It's not sophisticated game design, it's something a toddler could come up with. But sadly, these kind of cheap game mechanics are exactly what's selling well these days, just look at all those cheap smartphone games.