My 10yr old DW-5600E Casio G-Shock plastic strap started cracking, and I figured the battery couldn't be far from failing, so rather than change these parts and end up with a non-waterproof watch for half the replacement cost I'd check out what's new.  I'd always wondered when watches would self-calibrate themselves, and the time has arrived... they certainly can.

All in all I'm very happy with this watch.  I'd buy it again.  I'm marking it down for a few minor flaws.  If there was a 4.5 I'd give it that.

Feature comments:
* The case on this watch is the same as the old G-Shock I had, so I wasn't facing more bulk or thickness.  I'd rather it was thinner but its OK.
* Illumination system is the same (good), except it has an optional auto-illuminate function that works by tilting at right angle... useful in some cases but runs the battery down faster.
* I figured these watches would run almost forever if batteries weren't an issue.  Being solar-charged solves that problem, but whatever replaces the normal battery no doubt has a lifetime too.  My guess is it will be over 10 years... but it will take that long to know.  I've had the watch over a month and it's still fully charged.  Can't tell if getting enough light on it will become an issue over time.
* I was wondering if the radio signal would reach the Pacific Northwest OK, but other reviewers said it did so I took a chance on it.  The calibration cycle runs after midnight when radio signal is optimal.  Yes, it calibrates every night if I leave it on a dresser/table, but it never does if I leave it on my wrist.  Nor does it sync in large commercial buildings & hotels (steel frame.  This model only sync's in the US and Japan, so a world traveler won't get time-sync benefits when away from US.
* Accuracy is to within a second all day (checked against cell phone, DVR) when it calibrates at night.  Haven't tested its drift.  Have to get used to a watch that doesn't drift... my old watch being fast always gave me a little time-grace.
* Count-down timer is only 60 minutes, one of the biggest downsides to this model.  I don't know why the designers think this limitation is a good thing.  Has lots of alarm settings.
* Numbers are slightly larger, which is good.
* Can't see both day and date, a change from old model.  Annoying but keeping track of the day isn't usually an issue (at least for those who work).

Update 18 May 2012:  Has never dropped below full charge, and I work inside a lot.  Usually sync's time signal every night.  I'm getting used to a watch that's always right to the second.