Play it if: you've sort of failed to see the point of hypertext up until now, for this is an accessible and wonderfully creative use of the medium.
Don't play it if: if you roll your eyes at any poetry that tries to deal directly with the concept of transcendence.
This is the first hypertext game I've played that really made use of the medium in such as a way as to make me feel the medium itself was necessary to the story. This probably says more about my shamefully lacking experience with hypertext than it does about any transformative aspect to this work, but contextual considerations aside Ex Nihilo is more than worthy of praise.
The title is a reference to the Latin phrase creatio ex nihilo, literally "creation from nothing" - a rather slippery philosophical and theological concept about how we came to be. Appropriately enough, the game takes an immediately theological bent with the introduction of the PC as a godlike entity; progress is made less through actions and more through the determination of the entity's moods.
The game - I know it's not the best term for this sort of thing, but I dislike the term "work" and try not to use it - isn't particularly long or detailed. What it has is emergence. A major theme here is symmetry, and it is both explicit in the visual presentation and implicit in that the choices you make are mirrored, though not in any straightforward way - down to the final move of entering a text message and thus actually adding something to the world of the game (which, if you consider the universe of the game to be a closed system, really is an instance of creatio ex nihilo).
The result is that we have here something which feels genuinely responsive, where you really are being asked to participate in something rather than spectate. A lot of interactive fiction pulls this off like a magic trick by getting the player into the head of the protagonist and providing them with moral agency; Ex Nihilo is almost breathtaking in how much more real the creativity feels.
Will Ex Nihilo transform your life? Not really, no. But it's a beautifully elegant, elemental use of the hypertext form, and it feels complete in a way few stories ever do.