Another SG2 here. I love the SD card, the plastic body, the replaceable battery. Plastic and the replaceable battery help the phone surviving drops because they discharge the kinetic energy (google bent corner iphone or mac). Because of that I won't buy the SG6 when my SG2 dies but hopefully that will happen many years in the future so Samsung have plenty of time to rethink their design.
Other things that I love: the relatively small size, which let me fit it inside my front pockets if I have to, the light weight (but now only 20 g less than the S6, large phones are getting slimmer) and that I can mount it as a disk over USB without going through the MTP madness. A not so nice thing: the SD card is hidden under the battery so I can't eject it without shutting down the phone. This is a bit limiting.