"Fairies in Arcadia" is something of a pun here, since "arcadia" is a term we use to mean "games of a style you might find in the arcade" and, of course, has the conventional meaning of a place of peace and simplicity. It's apt in both senses, since The Great Tree is a simple skill and action game with a charming aesthetic -- and more depth than most games sold into the casual market, though without the degree of challenge that core gamers might prefer.
In The Great Tree, you're a fairy, and your task is to gather pollen to nurture the eponymous Great Tree, which apparently shelters your kind. Pollen appears as glowing points, drifting about the screen; you move your fairy with the mouse over the pollen to collect. When your "ponytail" is full (visual and audio cues make this clear), you take it to a circle at the top center of the screen to deposit it, and when you've gathered enough pollen in this level (there are a hundred in total), you score points and go onto the next level.
Various bugs flitter across the screen, each species with (in shmup fashion) its own pattern of movement; if you intercept a bug (or vice versa), you suffer hit points. In principle, you can die in the course of a level (which simply takes you back to level start), but in practice this is, as you might expect, a game tuned for the sensibilities of the casual game market, meaning it's awfully hard to fail.
Among the things drifting across the screen are "Swee," which are, in effect, powerups. To free them, however, you have to collect little green dinguses from some of the beetles, then use them to unlock the powerups. When your ponytail is full, you can also (once) click the mouse button to trigger an attack that kills nearby bugs; freeing Swees and killing bugs provides points that, between levels, allow you to improve character stats. At various times, you're also awarded "new wings" that improve your performance.
Thus, The Great Tree is a light but entertaining little game with an approach well suited to the feminine sensibilities of the casual game market, but with enough depth of play to appeal to core gamers. In fact, the feel of the game is an interesting compromise between the two: the casual game market tends to prefer "lean back" games that provide relaxation more than challenge, while core gamers prefer "lean forward" games that reward attention and skill. The shmup-like, real-time, arcadey nature of the game does require you to pay attention and respond quickly -- but it's quite difficult actually to fail. Of course, there's always the challenge of maximizing your score within each level.
The art is quite pretty, and the music well suited to the game's aesthetic; the one jarring bit is the initial voiceover narration, performed by someone who sounds like a bored Midwestern housewife -- perhaps indicative of the game's intended audience.