Well, let me get one thing off my chest first: Considering it comes with three pre-installed fans and the ability to adjust their speed, the Antec GX500 is a cheap chassis. For just 50 US dollars or 40 euros, the competition usually only includes one such unit. So the GX500 stands out in that regard. There are, on the other hand, plenty of companies that use the same approach, like Sharkoon. I cannot say anything for their quality, though, as I have yet to review a case that fits the same bill.
Everyone unfortunately has to make some money somewhere, which has the chassis suffer a bit in terms of quality; that is, if you look at what you can get in the 40-50 euros range if you forfeit a large number of fans. The Antec GX500 does work, but you have to invest a bit of extra time here and there to really make it look clean, for example. I would have loved to see real zip ties instead of wires as zip ties would have really helped. Users will also have to watch the length of their optical drive while using a full-width motherboard with the chassis.
Antec ultimately runs into some tough internal competition with the GX700 as it only costs around 10 euros more. While it may not offer as many fans, it looks good and makes much better use of materials. That brings me to the main point of critic: The GX500 does not fit into the GX line, not one bit. Antec could have expanded on that military look by bringing out a full-tower or military themed ITX cube, which would have nicely covered a few user scenarios, but has instead gone for a plain black chassis that has nothing in common with the GX700. So where does this leave the GX500? It, simply put, feels very much as though Antec simply put a case together at a factory to stuff three fans into it and place their logo on the front, and Antec probably made it a part of the GX family afterward.
To wrap up: Antec's GX500 is affordable, comes with three fans, and has a fan controller built in, but it no longer has any of the Antec genes as it drowns in a sea of similarly priced cases with its similarly simple look, similar feature set, and similar compatibility.