For what it's worth (and with no spoilers), there's a lot happening under the surface that's not obvious in volume 1; it reads very differently if you go back to it after finishing the whole series. Like you, I was initially more curious about the twist at the end than captivated by volume 1 overall. I let it sit for a while before I decided to read on. But after volume 2, I bought 3-5 the same day and read them all. (Volume 6 wasn't out at the time or I'd have gotten it then too.)
If you're not hooked after volume 2, then maybe it's just not the series for you. But I'd highly recommend giving it that second chance.
If you're not hooked after volume 2, then maybe it's just not the series for you. But I'd highly recommend giving it that second chance.