$255 for 45 minis (49 but 4 are token-style little things), is...ok? If you add in that it is a full, self-contained game, I think it is an alright amount. If you look at the Saturnine starter set for HH, it is running at $322 for 50 models. Saturnine comes with 2 characters, a dread, 6 termies, and a gun platform along with various marine bodies versus the 11 character/hero minis that Darkwater comes with. Whether that is worth $70 more seems like a personal opinion, but for the price I honestly think Darkwater isn't that bad. All of the minis look pretty good, especially the Nurgle ones, and I can see a lot of people picking them up just as cool painting projects.
Now, I'm not an AoS player, so I don't know if any of the models are playable there, but I have a feeling that most if not all can be subbed in as various characters/units or used in addition to others. 11 of the minis are character/hero models, so if GW was just to release those solo you'd be looking at a minimum of $385, if you count heroes getting the $35 individual model price.
Personally, I only really like a couple of the models for conversions, as that is what I usually do with AoS models- convert them into Necromunda or Imperial Agents (Inquisition weirdos). I also don't really play this type of game (I play 40k, Necro, BT, and Trench Crusade) so the box isn't for me. For someone who is into boardgames or is maybe not a gamer but looking to get into the painting/modeling aspect, I think there is a lot to like with Darkwater even at that pretty high price point.