I'm not GUM based but I lived there for a few years on active duty and later a few times temporarily on ADOS, as recently as about two years ago. Can confirm the naval hospital is excellent and extremely quiet for a military hospital that size; it's just about full service in terms of what it offers and in all the times I went there or took my family there, there was very little wait for the ER or for specialty referrals. Really one of the best hospitals to live near if you're a retiree and/or you've got a family.

Not terribly familiar with Andersen but NB Guam has an excellent commissary and NEX that is larger than a typical navy exchange and significantly cheaper than shopping in town, even compared to the normal savings CONUS. Decent hooch selection. Gas is also cheaper on base, and the housing is excellent. Not sure either if retirees are eligible for long term housing but I can confirm that retirees are eligible for short term (<30 day) housing in the NGIS duplexes and the hotel there. Highly recommend the duplexes; most are on Anchorage Court (off Breakwater Ave; google it) and it's 2-3 bedroom duplexes with 1 car garages, AC, decent furnishings, nice little back yards. They make very good temp housing at a reasonable price if you're retired military and moving to the rock but don't have housing yet so definitely consider that; you can stay there until you get longer term off base housing. For NGIS, this really is pretty good, and better than the AF Inn over at Andersen. Base food on both bases sucks, to be honest. Stick with making your own meals and especially avoid the Wendy's and the food court at NBG.

Any other questions from retirees/reservists thinking about GUM who haven't been there, feel free to PM me with questions too.