I don't think its too dark, I can still see whats going on, but sometimes its a bit tricky. I think you've got a nice way of showing the dark environment (its very atmospheric and pretty!!), but sometimes your characters blend in a little too much into the darkness, its sometimes hard to tell where a character ends and the bg begins. It may work if you add some lighter parts/backlighting around the edges which need it most. I do this quite a bit in my comic just because I think it makes whats important (characters) stand out at a glance
(eg from my comic
vs
)
Of course, my example is set when its still light, and i like the effect adding all these light lines gives in my comic, but if you maybe try going over some of the edges that blend with the darkness (i think especially around the characters hair in your example pages) with a dark blue line set to colour dodge or linear dodge (on photoshop, im not 100% sure about other programs, I think sai uses luminosity?) it could help subtly separate the characters from the background and help readability from first glance? Hope this helps!!