I guess I have something to say, having completed the Genocide route a few days ago and therefore having seen nearly everything the game has to offer.
Not going to repeat my general thoughts on the gameplay, I'll limit myself to the two extra Geno bosses. Undyne is pretty fun, even though I'm not a huge fan of the DDR minigame, the shmups segments were well done, and the ones with spinning concentric arrows were probably the most fun thing to dodge in the entire game. Sans on the other hand is mostly rather dull memorization, with tons of cheap crap that becomes trivial once you know it's coming. There's a few decent semi-randomized attacks there, but overall I struggled to clear it more out of boredom than anything else. At least the music was good.
The story itself is nothing special, what makes it good is very clever use of the metanarrative, in particular to make some interesting points about replayability and branching narratives in games. Undertale is the rare kind of game that openly argues in favor of certain design philosophies, which is honestly pretty cool, even if it ultimately advocates for feels over systems.
I do feel, however, that it undermines its own message somewhat with how the True Pacifist and Genocide routes are structured. True Pacifist in general is the weakest route in the game - it requires little to no additional effort relative to typical Neutral routes, and concludes in a pretty dumb ending, where the villain calls you an idiot for wanting to get the "perfect" ending (in which he is correct), and then the game gives said ending to you anyway through the power of FRIENDSHIP. I at least expected having to choose between saving Asriel and breaking the seal, or needing to make some kind of sacrifice resulting in a forced reset ala Nier. But nope, you win and everyone is super happy. I suppose the fact that this comes at no additional effort is part of the philosophy of trying to engage the player emotionally through aesthetics rather than challenge, but it still felt cheap to me. Best part of the route is the message you get after completing it and restarting the game (also true for Genocide, but that one has a really good ending).
The Genocide route, on the other hand, is where the "point" the game tries to make is expressed most effectively - it's the best written route, and what time is lost on grinding (somewhat remedied with the alt+tab trick) is regained by being able to skip all the boring puzzles. I actually think that putting the hardest boss fights in it goes against said point - they would've been better off in True Pacifist, and one-shots in Genocide just like everything else is.
On that note, I feel like Toby Fox simply lacked the integrity someone like VD has - AoD has difficult combat because that's what the game's central theme requires, period. I feel like True Pacifist is as easy as it is not because it makes thematic sense, but because Toby wanted everyone to be able to complete it and get their "best" ending and feels.
All in all though, I'll take Undertale's approach to videogame storytelling over any amount of walking simulators and linear cinematic action-adventures. One thing I'm wondering is, if Undertale is, after a fashion, an anti-JRPG, then what would like an anti-Fallout or anti-AoD look like? Undertale's criticism of C&C as a method of achieving replayability doesn't really apply to a game like AoD where player and character are strictly and explicitly separated, so I'm curious what a game deconstructing the Codex' favourite design philosophies would work like.