The story is kinda underwhelming, but it's not the biggest deal. I haven't unlocked all of Marina's dev diary, so, there are little tidbits I'm missing. The story is fairly simple, but there are cute little dialogue sequences between floors that reveal some more of the story and are entertaining.
My big issue is the gameplay. Sure, the whole "run" thing is neat but it can cause issues. One, in order to complete it, you have to beat the entire spire (30 levels) WITH A DIFFERENT WEAPON each time. This can become highly time-consuming. You also can't choose a specific level, you just have to pray you got the one you want when selecting the next floor, which hurts replayability (in my eyes, at least).
The level design is also plain. there's not much variation, and the levels are basically just arenas with a few differences. The game doesn't have many objectives to offer, so the gameplay just consists of playing similar levels and the same missions for 30 floors. Oh, by the way, if you die once (excluding Marina's hacks) you have to start all over again. From floor 1. Thankfully, I beat order on my 3rd run, but I don't want to imagine being a new player and trying out side order.
There aren't many bosses (about 3-4, I think), and their encounters are random (1 per each 10th floor, but the boss itself is randomized). So, you have to fight each boss lots of times, which gets tedious and sucks the joy out of them. By the way, do you remember that you can't manually choose a specific level/boss? Only the major story ones (2, to be exact) can be manually chosen... after you beat the game. Speaking of which, let's move on to the endgame.
The final boss resembles the first boss (Marina Agitando), where you have to destroy some portals to break the barrier so you can ink the boss itself. After you beat it, a cutscene plays and you have to spam ZR for a little. Then the fight repeats, but you have to destroy portals that hold color chips since yours were stolen. Once you break the barrier, you just have to attack Order. it took me at least 5 minutes because OH MY GOD HE HAS SO MUCH HP. I was using the roller and just circling him and spamming ZR. I kid you not when I tell you that I started drifting off. The song in the background started getting annoying because it's not very interesting musically. Oh, Pearl booyahs again but it lost the awe because it's not a killer wail and that idea was already used back in Octo Expansion.
The color chips are a neat system, though. They were probably one of the few reasons I tried to keep playing. It is fun trying to choose which upgrade you would like/need the most. The bonus and danger levels add a bit of spice, but they are far too in between. They made the game feel less bland and repetitive.

...But oh my god I hate the progression of side order. The gameplay gets boring after a long time due to little variation. 

That's not to say there ISN'T any difficulty. The farther you progress, the tougher the Jelletons become. (Or, really, they just spawn in higher numbers, have more HP [I think] and spawn stronger ones.) The missions also require more to be done, going from just needing two portals destroyed to four. However, with the tension that comes from increased Jelleton spawn rates, the missions are still very similar and don't offer much in terms of variation. 

So, if you are a new player, WAIT until you play this or you will suffer, because it is difficult.