Disclaimer: I am a friend of the publisher - I have gamed with them before and helped playtest the rules. Also, I actually read the document before release to help edit it.
Wonder is a no bells and whistles pdf - no art, and no graphics except a watermark and a few text boxes. The text is crisp and well laid out. The rules also flow well from one concept to the next and there are numerous links throughout to help you navigate. You get the rules, powers, a good example of play, a pretty good list of fantasy themed units, and a doc full of terrain templates that you can play with yourself to get the exact maps you want (cool).
The rules are simple and meant for quick fights between "minions" units only represented by their quality and "characters" who have four stats: quality, combat, defense, and wounds. While this seems too minimal to make it fun both minions and characters can have powers that can really make them unique. Mechanically all the stats are represented by different dice, from D2 to D12 giving you 6 different levels to play around with.
One of the unique features that I like is the Initiative and Action Point system. Not every unit will get to take action in a turn. The players bid for initiative and Action Points. The player with initiative can have their units perform some actions that the other player can't. Also, a player can spend an AP to interrupt actions of another player. This makes play really fluid and keeps everyone interested.
For combat - any units that are touching at the end of a turn fight. They both roll their die and the looser takes damage/consequences based upon the difference. Really easy.
You can really see some FATE influences in the game. From the battlemap which uses hexagon zones instead of distances, to minions only having one stat, and even the simple ladder system (though Wonder uses die levels instead of a bonus number).
It is like they mashed FATE and a wargame together, pared it all down, put a shine on it and came up with something pretty interesting and slick. Yes, it doesn't have art but it is a well put together product for a quick battle rule set. And it is PWYW released under CC-BY-SA. Excellent.