Google Now was introduced in 4.2 right? It alone is worth the 4.2 update. I admit that it is not that useful here in India but it still manages to do a lot of things and it would only get better with time.
In any case,
Android 2.3 was more or less feature complete. 4.x is largely a visual update.
NOT like that, infact from 3.0 (HoneyComb for
Tablets) onwards only Android natively supports multi-core processors for multi-tasking (means one process for Core 0 and another process for Core 1 and soo on). So multi-tasking on multi-core CPU was effective from HC for Tablets and ICS for phones... GB uses Core0 always for any task... (But still some 3rd party apps are capable of making effective use of multi-core cpus, eg: MX Player).
Similarly ICS has sooo many improvements over GB apart from visual and layout (navi key) changes. but the problem with ICS is its heavy and lags even some high end phones. But thats removed in JB (Project Butter -- UI @ 60fps). Infact JB can be called as ICS in steroids.. Other goodies in JB are GoogleNOW, Google Voice (kills Siri and S-Voice left and right), Photo-Sphere (3D Panaroma), Gesture typing in stock JB KB (like swype), Day dream (SS like), Lock screen widgets, enhanced notification (pinch zoom on notification list, reply SMS, call back missed call, etc) to name a few...
Infact transition from GB to ICS is very huge that there are very few phones from GB that got updated to ICS.. But ICS to JB change is not as complex as GB -> ICS, imho...