Great place if you check in but Changi is not great if you are the one waiting to see a plane off or arrive. Not a lot to do if you already had a meal with loved ones before they leave, and an hour or two before take off just trying to find a good spot to wait is so tedious. There is no viewing platform to see the flight off. There is a small viewing platform for planespotters, but that is not enough. I want the full tearful hanky, plane take-off or landing job - Nothing less is good enough.
I used to spend hours at airports as a child just watching from great viewing platforms in local airports and Narita airport is very well served. An uninterrupted view along a full outdoor viewing platform and an indoor one for bad weather - food and drinks, tables and chairs, take off and landing info - you can take photos of the main runway and they have a flower bed in the background so you can place the planes in context, should this be your hobby. Fantastic!

No fun seeing family and friends off from Changi really...plus a very confusing MRT ride for the novice. The times I have had to assist visitors to these shores to change trains to get into town, with luggage. Somehow it is not a good welcome for them. Once checked in though, it is a great airport, I love leaving from Changi!
Hey ho...