Firstly, this is a fine digital watch overall, ignoring the world-time function for the moment.  The light-powered function works quite well: it needs just a few minutes in bright sunlight (longer in other conditions) to become fully charged.  It keeps time accurately (gains 1-2 sec per month), and the display is easy to read, easier than many other Casios with busy dials.  I have mostly used Timex Ironman watches in the past, and this is as good or better, at a lower price.  The water-resistance seems to hold up well enough, but I wouldn't recommend using a 100M rated watch for swimming/kayaking/etc.  (Get at 200M or higher rated watch for that, I've had good luck with those.)

(The watch has the "module number" 3197, in case you want to find the manual on the Casio website.)

Now for the world-time functions: I was looking for a watch which could show multiple timezones around the world, whether I programmed them myself, or they were built in.  And I had some other criteria:
(1) At least six zones (some Timexes allow setting three zones), since I travel a lot, and like being able to just switch to the correct timezone instead of adjusting the time repeatedly.
(2) A good digital display, not analog or dual.  (I used to own a Citizen world-time watch, with a dual display.)
(3) Under $50 if possible, certainly under $100, so I could use casually/roughly without worrying.  (Rules out the Citizen and similar options.)

There were a couple of Casio watches that I considered.  One had a dial I considered too busy, with some "widgets" I considered quite pointless.  So I decided to try this one, thinking that the "solar-powered" would be a nice plus if it worked well.

I'm very satisfied with the watch now after having had it for about a month.  It was easy to set up, and it is sufficiently easy to switch to a different timezone when needed.  I find the plain black look attractive for a watch of this kind.  Contrary to some other reviewers, I didn't find that it looked "cheap", unless you're hoping to get something for $30 that looks like it cost $500.

What could be better?  Firstly, I think the display could have been even cleaner, without the lines across the dial, and a larger size for the main time display.  The date could have been shown as yyyy-m-d, rather than 'yy m-d.  The timezone scrolling could have been bidirectional (you can only go around west to east.  There could have been an option to hide some timezones you don't need, or that are redundant.  (There are several entries for the European timezone, for instance.)