Sound: I don't really care for the music, but from what I hear it's nice. Nothing groundbreaking, of course. On the other hand, the voice acting is really nice. It's available in 4 languages: English, Japanese, Korean, and Chinese. I've only heard EN and JP ones, and what I heard so far is really good. The main story is also fully voiced except SOME of the MC (us) dialogue.
Gameplay: well, it looks like tower defense, except we can move our charas, so it's more like RTS rather than TD. Also, the difficulty is not as punishing as Arknights. I've seen some recommending AK instead of this game, but so far this game doesn't force players (not me, at least) to look up stage guides in order to clear a stage like I heard many AK players say. However, there ARE some inconsistencies in difficulty. For example, players will experience a difficulty spike at stage 2-9 (for clearing the challenge) and then the difficulty will decrease again.
Another point against Arknights is the fact that this game respects players' time. It has the sweep system, held back only by stamina. So you just need to wait for a few seconds to collect the materials you need, compared to AK which doesn't even have auto repeat.
Storyline: well, it's the standard dystopian setting that's popular within this industry. The game also uses many of the usual plot device like "player is amnesiac". However, it uses those plot devices rather skillfully. Two chapters in, I can say that I like the story. I hate the characters that I'm supposed to hate, I like those I'm supposed to like, and I think there might even be some variations of the story since the player is asked to "choose carefully" at some dialogue choices. I don't know how big those variations are, or if they even exist, but it at least gives gravity to our choices.
Value: well, the packages look to be fairly priced. There's the usual battle pass, free and premium, with an l2d skin on the premium one. The monthly pass is also standard, $5 for one 10-pull spread across 30 days. I think I'll stay on free though, lol. For f2p, I think it's kinda good? I've been playing for less than 2 days and I've accumulated enough currency for 50+ pulls. That's including the free tickets I got from logins. Apart from that, the launch celebration missions gives you one S-rank, the highest rarity. That S-rank is also allegedly one of the best of all. Oh lastly, there's a discounted beginner banner that only cost 8 tickets to do a 10-pull, and what makes this banner great is that the first 10-pull is guaranteed to give you an S-rank.
The con for me so far is something at the start: you're only given access to all the launch gifts after clearing stage 1-4. That makes it harder to reroll. This problem is also exacerbated by the fact that there's not guest login AND a 15-day waiting period to delete your account. This means you have to create a bunch of e-mails (can't use salted e-mails) if you want to reroll.
That concludes my review for this game. It's worth a try if you like TD.
Edit: for those who want to start, try getting Langley. Dps is king here, killing enemy faster and earlier means you don't have to worry about the stage challenge (no SAN reduced). I settled on Zoya and I kinda regret it cuz she's melee, not ranged lol. There are some stages that forces you to use long range more with only 1 or 2 melee. If you don't want to waste time rerolling then that's okay, EMP is also amazing even if she's only B-rank.