I have been a long-time fan of Samsung... and still am. I love my Galaxy S5! It love it's battery life, I love that it's water resistant, I love how fast it is, and I love the features like Blocking Mode, Ultra Power Saving mode, download booster, and I actually use the health features as well. The sound quality also decent. Best smart phone I have owned so far...
I've heard some people express disappointment that Samsung might be moving away from expandable SD card storage and removable batteries. I'm not crazy about this decision either; however, if you asked me how often I change out the SD card in my phone, I'd have to honestly say never. Same is true with the battery at this point. Though I have replaced defective batteries in older Samsung models. In the one case, it was because the phone got wet and destroyed the battery. If Samsung makes the 6 waterproof, then I would suspect the battery issue would be less of a concern. There are also cases available for the phone that have a battery built-in the case, which accomplishes the same thing without needing to touch the phone's battery and with chargers providing much more rapid charging than in years past, I can't see this being a big deal. I just always thought it was cool that you at least had the option with Samsung, where you didn't with Apple.
Call me old-fashioned here, but I really miss the phones having FM transmitter's in them. I know almost everything is Bluetooth these days, however, there are many situations where the old FM transmitter would still be quite awesome. For example, riding in a car that is not equipped with a Bluetooth radio. This actually happens a lot still. It would be cool to still listen to my phone's playlist through the car's FM stereo in those cases. I know there are devices that can be purchased to compensate, but I don't want to have to plug in a bunch of other crap, I just want to use my awesome phone that does everything! I really miss the FM transmitter and it seems like it would be so simple to bring it back.
There's my 3 cents. Thanks for the post question Scott!