I'm still on the Pre-Alpha version of ICS, never bothered to update since I knew Shishir would release a new base soon enough, so my list may be outdated. So I'm including more than three, sorry xD but first three are my top three, give me those and I'm really happy already.
1. Fix for the increasing ringtone (probably already implemented)
2. Stock Samsung lockscreen, or at least one you can set your own wallpaper to (also probably already implemented, I've got AOSP lockscreen but with setting wallpaper function was broken)
3. Stock Samsung Gallery so you can attach multiple pictures to one MMS, and so you can attach existing ones from the stock Samsung messaging app itself rather than going through the gallery (I've got the AOSP gallery that came with Pre-Alpha ICS, and that broke these functions so whenever I want to send a pic I've already taken I have to go through the gallery, and I can't send attach than one picture at a time)
4. Scrolling wallpaper (I heard it wasn't part of the GS3 launcher)
5. Ability to set which homescreen is the default home one that you go to when you press home button (not available on international versions of the GS2 launcher, at least that's how it used to be)
6. +1 for the option for old slide-down notifications menu, I like sliding it down partially to quickly read a text then flicking it back up without having pulled it fully down
7. Ability to enable/disable home button lag and enable/disable the double press to launch voice commands (not a requirement, I know you can set the search button double press to any voice command app)
8. Some of the
GS3 functions such as Smart stay, Smart alert, Direct call, S Beam, S Voice, AllShare Play/Cast, etc. (just dream ones, also probably battery drainers).
There you go Shishir, hope that's enough feature-asking for you. If it's too much and it sounds like I'm being a self-entitled, pretentious, whining, can't-contribute-anything-useful kid for asking all this, go ahead and flame/yell at me, I'll gladly welcome it after this post XD