Funny you should say that, it seems most have no problems with the new software. No software experience is perfect, and in the end I prefer facts to measure performance. What I perceive isn't running smoothly could be far from the truth. Apps refreshing may look like it's an issue, but what if the overall time to perform desired functions is still faster than the rest. Here's a shootout using real life tests.
http://www.tomsguide.com/us/fastest-smartphone,review-2881.html
So, of those 9 tests, 4 are benchmarks, another is video encoding (yup, we're all doing that everyday), and the last one is wifi speed test--of which all phones are achieving data transfer rates far faster exceeding the speeds the vast majority of us will never see on any networks we connect to. Yes, those are perfect representation of the everyday use of a smartphone.
This shootout is a perfect example of exactly what myself and others are talking about. We're not disputing the hardware Samsung uses isn't top notch--it's almost always near the top of the benchmark results. The display is industry leading and the camera on the S6 is arguable the best available on a flagship smartphone. What this 'shootout' doesn't show is widely reportedly memory issues, the documented lag in app switching (plenty of videos over on YouTube illustrating this), the often subpar battery life many (notice I didn't say all) are reporting, or the general malaise many of us have with the overall UI design.
And what about the Note 4 issues Spinedoc mentioned (also, very widely reported) since updating to Lollipop? Same hardware that was running KitKat--all that's changed is the software. Maybe the Android base software is too blame? I don't know but a great many of the other devices that have also received Lollipop are reporting better performance with each Lollipop update. Why is the Note suffering so badly?
Nobody here is claiming the S6 is a bad device--it's likely the best Samsung has ever made. The problem is that with the hardware and horsepower is has 'under the hood', it should be blowing away everything else and that's simply not the case. What I don't understand is that it's the same tune every year--why can't Samsung see it?