In the hidden-object genre of casual games, there's a substantial and largely regrettable subgenre of romance-centred stories, within which are a few games about planning weddings. In certain respects, D-Day plays very much like Dream Day Wedding and its ilk. The gameplay mimics hidden-object in that there's effectively nothing to do except to find all the things and put them where they need to be. To-do lists and now-do-this instructions strive to preserve the player from the slightest confusion. The world is sparkly and conflict-free, and the bride is kept safely generic; her intended is absent, barely mentioned at all, and seems irrelevant to the whole undertaking. (It's probably unfair to consider D-Day as literature rather than a straightforward iteration of a standard fantasy; it's certainly not attempting anything more than the latter, which means that I'd be unlikely to like it much regardless of its other qualities.)
The two key elements of casual games that it lacks are a high level of aesthetic polish (in IF that might translate to lavish prose and meticulous scenery implementation) and an intuitive, idiot-proof, silky-smooth user interface. Both of these could have been substantially improved by testing.
It's probably fairest to think of D-Day as a My Apartment game. In that light, it's quite respectable: it demonstrates some thought about structure, it provides immediate objectives, it's trying to be considerate of the player, it can be won without ever getting stuck, it doesn't have the cynically lazy my-game-sucks attitude that typifies My Apartment.
A just-so story: an author has some small children. Every night, at bedtime, he sits down with them and invents another installment of an ongoing story. The children chip in with suggestions. The story they tell has a lot of problems -- exactly the sorts of problems you get with stories told off the cuff. It's mostly a series of fragmentary set-pieces, it's heavily derivative, it lacks cohesion, there are a lot of loose ends that never get tied up; the stories are mostly unified by a broad setting and recurring characters. The children don't care about any of this, because they're sharing a story by their dad. Later, the author assembles some of these stories into an IF game, designed to be accessible to children. Whether this actually represents how Alabaz was written is irrelevant: it's very much how it feels.
The plot: you are an Everyman child hero, tasked by the fatherly but inert King of Alabazopolis to reunite an archipelago-kingdom sundered by mists. To do this, you must take your child-crewed ship, explore the islands and recover magic pearls; there's more than a touch of anime about the scenario. Its strength is in its set-pieces, which include plenty of strange and striking imagery. (Some work much better than others.) The novice-friendly design is a more questionable virtue; the influence of casual gaming is obvious, with heavy-handed pointers and showers of achievements, and a character whose main function is to follow you around dispensing tutorials.
Despite this, Alabaz is consciously old-schoolish; it's a substantial size, and there's a lot of Zork and Myst here. As a game for children, its worst structural flaw is that it's a big-map game that's designed in ways that make travel very tedious, even when you've solved all the relevant puzzles. Apart from this, the puzzles are solidly designed and appropriately easy; but I think that this was intended as a game to be played over many evenings, which is hard to do with easy puzzles. The tedious navigation fills that gap.
In terms of content, there's a sort of uneasy dissonance that a child might or might not pick up on: it's a world where adults behave like sulky children and children behave like responsible adults, and it's also a world that promises heroism but fails to deliver, because heroism requires real monsters, and in Alabaz all apparent monsters quickly turn out to be paper tigers. The game seems designed for very small children -- too small to cope with very much conflict in their fiction. I can't say how well it'd work for its target age, but there's a great deal that makes this translate poorly for adults.
I suspect that children’s literature is best written not by a doting parent -- someone who primarily wants a safe, clean, improving world for their children -- but a crazy uncle, someone who wants to entertain, inform, subvert.