That sounds like a great offer. Very few people get offered houses in Dun Laoghaire Rathdown. Goatstown is a grand area and I imagine that Goatstown Close will be a nicer development than a lot of the larger apt block schemes - some of which are very high density, grey and boring.
Just make sure you get an independent valuation and question the market value if you think it's too high - be sure and put it in writing because you get a no on the phone, a letter gets a better response.
Good luck with it!