I have been playing around with the faces on the Apple Watch and so far I have settled on four favourites:
Simple : Chronology : Colour : Utility (below)
Having tried out a few of these and having tweaked them using the customisable options, it does seem that there is so much more that Apple can do here. Most of the faces above are quite similar and there does seem to be limitations on the design due to the battery life. For example, there is no way to choose a different colour background. So if you attempt to recreate a watch face from another manufacturer (such as the example below from Seiko) you will be out of luck:
Presumably a blue background would mean more battery power as the whole face would need to be lit in colour and this would reduce the number of hours that the Apple Watch would last. But as the Watch develops and the batteries improve this will surely be an area which Apple can develop.
Also when it comes to the face, it will be interesting to see if third parties will be allowed to have information displayed, such as a news headline at the bottom of the screen or a to-do item from your favourite reminder app. There are even parts of the Apple information which cannot appear here- one example is heart rate. For now you can only add time, world clocks, date, activity, battery level, moon phases, stopwatch, alarm, weather and stocks.
For now customising the Watch face seems limited and this is due to battery concerns. But it does mean that there will be a huge range of options which Apple can add in future updates or in the next generations of the Watch.