As others have noted, it would be difficult to avoid presenting spoilers for this work unless pretty much the whole review is wrapped in a spoiler tag. So:
To start, I want to make it clear that (Spoiler - click to show)I came across this work as a result of the "Doing things backwards" poll here on IFDB, so arguably I came to it pre-spoiled. I believe that this actually increased my appreciation of it, though your mileage may vary.
I didn't find many other reviews of Keepsake in my cursory search, but a couple of the ones I did see indicated proofreading and/or debugging were needed. The version I played this evening (yes, this is a fairly short piece) was release 3, and I saw no evidence of any such issues. Both the coding quality and the writing quality felt above average within the story's limited scope.
There are two things I really liked that I think speak to the author's potential. Neither of them is the overall concept itself(Spoiler - click to show), which the author makes clear is inspired by the film Memento (from which the title is derived via synonym).
First, the opening sequence does an excellent job of plunging you into the role of protagonist. The leading quote very subtly frames your expectations about the kind of situation the PC is in, and a few deft touches in the details set up the tensions of that situation very well(Spoiler - click to show). I love the way the initial description of the brass casing practically screams that you need to start cleaning up the crime scene, but a few simply-repeated words ("the sirens are getting closer") scream just as loudly that you need to get out NOW. It was a great opening(Spoiler - click to show), it's just not the opening that goes with this story.
Second, the first encounter with the central mystery is extremely well done(Spoiler - click to show). In the alley scene, the author has taken great pains to ensure that descriptions of things and events are precisely ambiguous enough to work whether you do or do not understand what's happening, i.e. whether they are presented forwards or backwards. It quickly becomes clear you are being given a choice, and it's not hard to work out how to make that choice.
Unfortunately, after these first few minutes of gameplay, Keepsake falls apart. Emily Short cuts right to the heart of the matter when she asks "[Do the choices the player makes] matter? What story is told by these details?" Gimmicks are not necessarily bad, but carrying this one through to the point where people would stop referring to it as a gimmick would probably take a mind-numbing amount of work in both the writing and coding departments. It almost seems that the author realized exactly this mid-project then just decided to wrap things up and be done with it.
The only thing that looked like a mistake at a high level was the epilogue presented once the story is finished(Spoiler - click to show). While I appreciate the effort that went into it from a technical standpoint, the effect is similar to playing Memento scenes in their "correct" chronological order... that is to say, it pretty much ruins the story completely. Rather than providing an instant replay of the scenes already seen, some other device (a police report reconstructing the protagonist's actions?) is called for to reveal the mystery. Then again, maybe my perspective here is driven by the fact that it wasn't really revealing anything new to me, due to knowledge beforehand of the story structure.
Again, I remind readers that my rating system is unusually harsh, and the two-star rating does not mean that this piece isn't worth the time it takes to experience it. Keepsake shows the marks of real talent: If what's on display here were paired up with more attention to story construction and consistency of player experience, I would expect to see future efforts from this author perform much better in the IF Comp.