The start is mediocre and it only goes downhill from there.
I might be a bit harsh on something that's basically just soft porn but it's not even doing a good job at that. The story to ecchi ration is far to high for this bad of a story.
It goes and poorly explain things that didn't need explaining and leaves other, more important things unexplained.
The ending specifically is just bad. They forced a sad ending for the sake of one (it's like the author never heard of inbreeding).
It's sad that early on there were some hints of a greater story that makes you wonder what will happen and gives you hope that something cool and interesting will happen. Shame it's disappointing when you get to it.
But at least they didn't leave it unexplored like in some bad mystery stories so I guess that's a plus.
Altho anything that you'd assume is going to happen is probably better than the actual plot.