Great series! It had its flaws but after ascertaining the main plot I thought I wasn't going to like it too much but I actually really enjoyed it.
I think MagEarwhig brought up one of the bigger flaws with the series, which was that Hiiragi had almost no development whatsoever despite the fact that he was the "leader", they didn't even really explain why he was a bad leader (Rin guilt tripped him but it wasn't clear why what Rin said actually meant anything to him), plus he also supposedly loved Mokuren yet unlike Gyokuran who was very verbal, or Shuukaido who was observing quietly he never actually did anything.
I feel like the ending might have been a tad bit rushed but honestly, the drama, and the aspect of these past selves projecting themselves on their present reincarnations through dreams, coupled with the fact that the past selves were a group of seven researchers from another planet that had quite a bit of drama up in space, actually made the whole thing quite interesting to read despite it not being what I would normally consider a great read.
Overall I really liked the series and would give it a 9/10, maybe 8.5 considering the flaws, but the fact that what it did do well, it did so much better than most other manga, I think it deserves a 9/10.