Keep us posted brother.. I'm hearing aggressive app and ram killing on early reviews..
It is real hard not to be a fan of it. I had a Note 3, but have had Nexus devices since. I loved my Note 3, but Touchwiz was never great for me. They have really improved it, with some minor head scratchers. I miss my AOSP volume profiles, just one push of volume button and and you can choose Priority or No notifications. I used that, but can get over it. I do like one volume down push gives you the option to choose from all of your volume levels.
My Spigen case should be here tomorrow or the next day and I can ditch this crappy case Bestbuy had, just had to get it in something. If I am keeping it, will need to get the At&t globe off the back, though don't want to scratch the glass. I am sure some S6 owners already have a way to do that, so I will search that out.
It does seem like it does not like leaving things hanging out there in memory, which I don't mind. Yet recalling apps from recents, or even loading anew is very fast. The only lag I have seen on the device is because of GEL, scrolling back and forth between the Google Now page, and it was minimal.
It is actually smoother than my Nexus 6 when it comes to general UI stuff. I miss my Hotspot quick launch, but I am sure an aftermarket app can bring that back. If I could kill the constant WIFI notification without root, I would be pretty happy. Did some searching on that and killing the settings app does not seem to be working for this one. Nor do I know what other consequences that might have.
Multi-tasking works great and you don't realize how useful that is until you have it. One of those things you don't think about until you need it. Helps for work stuff, copying and pasting between email and Skype for example. The S-pen screen write is awesome, pulling the pen out with the screen off, writing a note and putting back the pen to turn the screen back off. I can see where that will be very useful for some people.
Anyway, I am rambling, just some general thoughts. If anyone has specific questions please shout and I will do my best to answer them.