I have been using Android devices since the very beginning and now I am on Samsung Galaxy S3, which isn't even the latest phone, but with the latest AOKP KitKat 4.4.4 ROM it works incredibly well. It looks like Android has improved so drastically since the first release that its hard to even consider it the same OS, although AOKP changes may have contributed to that feeling. The way it is streamlined today and cohesively organized almost rivals iOS's smooth user interface, but without the iOS restrictions. Frankly, iOS has little to no advantage in comparison to Android KitKat 4.4.4 and even less after Android L will be released. Everything just flows on KitKat. I hope this trend continues!
I was checking out new features of Android L and the external UI changes planned seem so incredibly... small? Adding a shadow under a Lockscreen widget/window or changing to some specific font or even changing some icons are not really reasons to release a whole new version of Android IMO, but again, its these small changes that made Android the way it is today, making such changes very welcome I just hope there will be many more internal optimizations, such as ART optimizations, responsiveness increase, battery savings improvements, etc. One thing I really wish for is that Google releases some themes that re-create icons for practically all Google apps or top 100 Paid-For & top 100 Free apps out there or at least create a way for Themes to apply its settings to already existing icons. Right now there are no themes that can fully apply to all the apps I have, which is a pity and it gets in the way of the UI cohesion.
I wanted to upgrade to Galaxy S5, but it doesn't seem any more responsive than Galaxy S3 with AOKP. Internal hardware and Android still haven't reached that level where apps are instantly responsive with less than 50ms delays. I'm not talking about loading time, but once something has loaded, a menu button or even a "Close Application" button should instantly work without any delays, and once you're back on Home Screen or Menu/App Screen, you shouldn't have to wait another half a second before launching a new app is possible. I've tried SGS5 and the latest HTC and even latest iPhone / iPad, but none of them are as "instantaneous" as PC's with Windows 7 / 8.1 or even Windows XP. Those who have very fast high-end PC's with fast SSD's know what I'm talking about, although once in a while there are occasional delays even on such PC's. The reason to this is hardware of course. No Smart Phone can compare to, for example, Intel i7 4790K with 16GB of DDR3 RAM and Samsung 840 512GB SSD running updated Windows 7 or updated Windows 8.1.
Anyway, just thinking out-loud - probably in the wrong forum anyway!