Let's just start with this: The GLS100's are Winter G-Lides. "What does that mean?" Instead of moon phase (although that could be really useful) or tide graph functions, it is more physical differentiation. Low-temp modules, non-resin bands, etc. This technology isn't new and Casio has been doing this kind of stuff for a while. There are four watches in this series, I'll take a page from Clement Wong here (if you don't know, he is the BOMB for seeing upcoming G-Shocks!):
As you can see, I've received 3 of them. That white one also seems like a good looking piece (some people's favorite actually) with features similar to the one I'll call "blue" here though it is black with blue accents. The module is 3402 which has some interesting features. Double thousand hour stopwatch with auto-repeat. One nice thing is that it uses the "eye candy" portion of the face to keep track while you are in normal timekeeping mode. The Countdown timer is 24hr, set-able to the minute. Again with auto-repeat feature. The alarms seem to have a wide array of flexibility from hourly chime, to date + time, to only ring out in one month, etc. I don't think any of these are new features, but if they are important to you, click on the module link and see if it works for you.
I'm not going to make any pretentions of un-biased, showing no personal opinions, facts only so you can make your own judgement on these watches. I love them, so read my impressions accordingly. You have been warned!