The Galaxy S2 when it came into my hands was still on the old Android 2.3.5. Rather a clunky affair compared to what we're used to in Android today. I downloaded Kies and was pleasantly surprised to get an immediate notification that there was a update available to 4.1.2. This is the latest stock ROM for the Galaxy S2.
Kies is probably the cleanest way to upgrade a ROM.
The performance was better. Interface intuitive with email and Facebook notifications running seamlessly with the OS.
Google services a response to Apple's I Cloud is a fantastic in house restoring system apps warehouse.
I tried to update the ROM using a restore rom without sucess and Odin gave me the rescue I needed.
The initial setup is really good with apps associated with your Samsung and Google services account can have your phone back to where it was less than an hour.
Even though the phone is now 3 years old, it still stands good against the s4 and s5 on performance and battery. The lack of evolution to Android 4.4 is disappointing.