I swapped my S6 edge for my OP3. Couldn't be happier, there's no way I'd go back!
The OP3 camera is very good - easily competes with the S6 edge (fun fact - both are using 16MP Sony sensors - although some S6e's came with a Samsung one, but mine was the Sony.)
Battery life - night and day difference. I got serious buyer's remorse from the S6 edge battery.
Software - bye bloat

feels more like my phone the way I want it!
Performance - again, night and day. Super smooth phone. Also - and I'd include this in "Performance" - the fingerprint sensor is so quick.
Those were the key points for me. Looking back on my purchase, easily the happiest phone purchase I've ever made. My S6 edge was £750, my OP3 was £309. I'm still in shock. It's definitely built like a high end flagship and feels it.