The DW6600 has been one of the most popular G-Shock models worldwide ever. Along with the DW5600 and the DW6900, you can find it on the wrists of soldiers, policemen, firemen, paramedics, and all sort of professionals that need a dependable and rugged timepiece. You can find it on many laymen wrists too.
The DW6600 is a basic functions G-Shock: it has standard timekeeping with day, month, and date; a daily alarm, a 60 minutes countdown timer, and a 24 hours chronograph. Its basic version in black resin can be found very cheap in all sorts of online and real life stores.
There is an outstanding characteristic in the 6600: It has the most bright electroluminiscent backlight that you will ever see on any G-Shock. And rightly so, because this was the first G-Shock model that used the concept when Casio released it. It is something of a lantern, and you can almost read a book at night with it if you want.
Although it is a popular model, Casio has not use it as extensively as the DW5600 or the DW6900 for special editions. So when recently I saw a post about a DW6600 with a Scorpion background silhouette on the display in WUS G-Shock Forum, I, as they say, pulled the trigger. And I didn't regret it.
According to the G-Shock Perfect Bible 1983-2007 (Gakken Mook, Tokyo, 2007), the DW6620-2 (this model's exact number) appeared on November 1995. I was lucky to find a New Old Stock one, so its condition is excellent, but for a little yellowing on its clear blue resin strap.
This particular Scorpion is a Japanese edition, so as in others G-Shocks for the domestic market it has the words Fox Fire on its dial as reference to its backlight system (for export models have the word Electro Luminiscent Backlight, instead). Fox Fire is the designation of the bio-luminiscence emitted by some kind of forest fungus, and its blue tone is almost equal to Casio backlight's.
The 6620 Scorpion is a nice Spring time model, and its backlight is unique.
Note: Many thanks to Sjors for the opportunity to write this commentary, and also to Gregg for the hospitality.