A couple of days later I checked my inbox and I'd got lucky! I visited the Google Play store to download the game, but couldn't find it. It seems the game is "not available in your country". Go figure. So I googled around and managed to find the APK and install it anyway, and it turns out that I live in the one city in my country with a reasonable number of 'portals' that can be 'hacked' and I was on my way.
The objective of Ingress appears to be capture these 'portals' which are sources of 'exotic matter' and to place 'resonators' on them to power them up so they can be linked to other powered up portals. When three portals are linked to surround an area that area delivers a number of 'Mind Units' to the faction you are playing for - either the "Enlightened" or the "Resistance". As you level up you gain the ability to use higher level resonators, which increase the range of your portal links and you fairly quickly realise that the real power is in portals at the edges of the cities.
As a starting out player you can feel fairly powerless, but once you get going it is possible to build power fairly quickly, especially as you capture areas, which i the action providing the most 'AP' towards levelling up.
The game is still in closed beta at the moment and the full details have yet to unfold, but so far it's been fun. Having the portals located primarily on public artworks is a great idea and I've enjoyed finding a few new sculptures and murals I wasn't previously aware of.
At this stage it is not clear to me how the game will evolve over time. Will it run for a period and some faction be declared winner before starting it all over again? Will more rules and story become apparent and this just work up into one epic battle? From the way the hype is being managed it looks as though this will all become clear around the end of the month.
Meanwhile I better head off to defend my portals...