How's the story compared with the other translated Eushully games? I really enjoyed how simple the story was in Kamidori but Castle Meister bored me to death. The story just felt overly long and too padded.
Hard to say for certain, since we can't know your tastes as well as you do.
From what I remember from my first playthrough (back when it was still a raw MTL), the story was more heavy than Kamidori's. We are talking parallel dimension/reality, all-out war between Angels and Demons, dodgy scientific experiment, paramilitary group and you stuck in the middle trying to survive with your friends. What I mean is, it's not as light-hearted as Kamidori or Amayui.
Now, I won't say the story is complex (there are better stories and there are better VNs), but it's not straightforward either. There are differents factions working with or against each other, subplots and secrets to discover. I wouldn't call it simple. Not as simple as Kamidori or even Amayui. But then again, what do I know ?
As for whether it's boring or not, it really depends on you. I wasn't bored, but it's only my take. I really loved the world and the ambiance of this one, but it's true that it's very different from the usual fantasy settings of most Eushully's games.