Just finished watching the Sky Girls anime. The series started out as a single-shot OVA by Konami, and proved popular enough to be made into a full series by J.C. Staff.
The setting is centered around resolving a war between humanity and the WORMs, a strange type of enemy weapon. The WORMs are constructed of several cells that rearrange themselves into the shapes of larger creatures and wreck havoc on human military and industrial complexes. Their motivation and origin are a mystery at the start of the series, but are explored in fairly great detail as the plot progresses.
The first war with the WORMs left Earth in a fairly broken state, as WMDs were eventually used to try to stop them. In the aftermath of the fighting, much of Earth's landmasses have been rearranged, and humanity is only just starting to rebuild. The main characters come in at this point -- due to a lack of military-age personnel still in existance, the average age of most soldiers has been heading downwards. The main characters are chosen for their ability to pilot experimental aircraft, the Sonic Divers.
The Sonic Divers, at first, are explained to be designed for various uses, but naturally, as the series progresses, their main function is to perform as a weapons platform. The WORMs reappear, and the Sonic Divers are equipped with a particularly effective weapon for destroying them. The reappearance of the WORMs is somewhat of a myster -- they were meant to have been eliminated much earlier on, and a significant portion of the plot is dedicated to figuring out what purpose they exist for.
Sky Girls is particularly interesting due to the fairly extensive amount of character development present. It makes what, at first glance, is a fairly standard mecha anime into something far more character-focused. Even secondary characters get a fair amount of screentime dedicated to their motivations and backgrounds, and a viewer's first impression of a character can often be fairly off from what the character actually is like.
The technology shown in the anime is fairly internally consistent. There are reasons why specific pilots are chosen to use the Sonic Divers, as well as why the Sonic Divers were designed in that specific way as well. There isn't too much tech-speak, and the reasons behind all the designs are not difficult to grasp (though as with most science fiction, there's an element of handwaving with regards to theories that have not been defined in real life).
The animation is fairly good, and the music is decent. There's a few instances of fairly obvious 3D CG works, but they do not detract from the animation as a whole, as it's blended in fairly well.
All in all, the series is quite worth watching, being well-written and with amusing enough characters.