To give some context here, the main attraction of IF for me is the storytelling - I enjoy the odd puzzle, but not half as much as a well-told story. The storyline of Shrapnel is interesting but not ground-breaking; Shrapnel's strength lies in its medium. The choice of IF over paper and ink pulled me forcefully into a narrative that I might normally have dismissed as "not my thing". Moreover, it's a story that I plan to read again, or at least skim.
I approached Floatpoint as a story, rather than a puzzle or a game, and it met all my expectations and more. I'm fairly sure that even if I'd been reading it as a linear, fixed narrative, I'd still have enjoyed it; but the fact that I could influence the ending (towards what I felt was the right thing to do) gave it an extra dimension.
For context, I'm a great fan of short stories, and of the kind of science fiction that focuses on how the snazzy futuristic situations affect the people who find themselves in them. Floatpoint hit all my buttons. I just wish my memory was less vivid, so I could play it again sooner and try for a different goal!
(I should also note that in contrast to Valzi's review as of 27 October 2007, I didn't encounter any bugs.)