There was a discussion on Cityside on these pages a few months ago, it might be worth your while having a look back to that earlier thread.
IMHO both of these developments, although they contain some nice housing units, are a bit isolated. Cityside is a good hike, rather than a walk, away from Finglas Village - you might be near the M50 but you're not that near a pint of milk, not until they supply the promised services anyway! But on the other hand, although Finglas has some drawbacks, I'd much rather live there then miles outside of Dublin, if commuting is an issue. It'll take a few years to see how these areas are going to pan out, community wise - but as many other posters have pointed out, crystal balls are one of the few ammenities not available on AAM!