I also enjoyed Geist .
However, the main flaw that game had were the controls. At the time that I first played this game, I had already played Metroid Prime, Time Splitters and XIII, among many other FPS/FPA games. And I was disappointed at how Geist was rather hard to control. Almost every action had me fighting with the damn controls, instead of me concentrating on the game. And this was quite bad, because you had to be very quick with switching bodies (or possessing an inanimate objetc). Some boss fights were extra hard because of the lousy controls. I wish if they ever make the sequel, that they please get them right. I mean, if other game devs got it right on the GameCube, so many years ago, certainly they can do it today. Especially when Heroes of Ruin has fantastic controls on the 3DS (and without the use of a CPP!).
Another thing that I hope they can enhance in a potential sequel, is the possibility of possessing many hosts/people, regardless if they're vital to beat a level. But only to have fun, like making them get into trouble by having them do crazy stuff. And then leaving the poor sods to deal with all the flak. The original Geist limited too much what you could do. It was too linear in that sense.
I know they can do better and hope they get a chance to get it right.