I've only had mine over the weekend (launched Friday where I live), but I'm very impressed. Seems about the same or slightly better than my 7 Plus was, which is mighty impressive considering the battery is smaller!
Really loving the 8 Plus and it's definitely the phone for me, until the X's tech reaches the Plus models. Loving all the little improvements. True Tone, louder and bassier speakers, camera is surprisingly better. Taptic Engine also feels a bit nicer, less 'buzzy', if that makes sense. I also love the haptic feedback in the Camera app!
True Tone is the killer feature for me, though. I know it won't be a big deal for many, but I consider it to be a massive upgrade. I put it next to my 7 Plus and was quite disgusted by the blue-tinted display of the older device!