What makes it worthwhile for all the trouble in upgrading from GB 2.3.6 to ICS 4.0.3 on an unrooted S2? Any feedback is much appreciated
Supposedly the main features of ICS4.0.3 are outlined in
this section of wikipedia... and the improvements are quite huge and aimed at better operating system management and some graphical upgrades and tweaks.
However... (and this is not to scare you in any way)
Considering the upgrade is a huge undertaking, you may encounter a lot of problems due to the difference of firmware versions... (this is installing an entirely new OS from GB to ICS) and may require to do backups, upgrade, factory reset and restore your data... some apps and game saves may not be successfully recovered by your backup as most likely its going to be stored in the firmware data partitions that will be wiped out by a factory reset (unless they have a game data export function - but that's unlikely)
Considering ICS is still in its early development, you're likely to encounter annoyances like bugs from programs designed for GB that haven't got an upgrade and thus, may FC often, some features not yet properly implemented (like bluetooth pairing authorization... GB has lock permissions on a paired device when transferring files through BT, while ICS doesnt and requires authorization everytime you send a file), you may encounter flickering light issues, sudden reboot issues (if you dont do a factory reset after upgrading) battery and heat issues (partly due to lack of factory reset), wifi and network connectivity issues, you may (rarely but some people encountered it) even lose critical data like your phone's IMEI, you may have low network reception (compared to 2.3.6), some apps may fail certain functions which can be an annoyance (like facebook photos syncing with your phone's contacts - which results in no pictures from fb) - but these are small annoyances, but if you're really into overall stability and convenience, I personally suggest not to go with upgrading just yet.
But honestly its all about you... upgrade to get the latest OS features but encounter problems usually associated with a new OS, or wait until there a more improved and stable ICS to consider upgrading to... and let your desire to upgrade eat up your soul.