biggest thing is probably XP couldn't really do 64 bit. (sure there was a 64bit version of XP, but the driver and software compatibility of it was crap, and Microsoft never really supported it.) Proper 64bit support came with Windows 2003.
While there are things I still dislike about Windows 7, such as the network and sharing center, the amount of disk space it takes up compared to 2003, how resource heavy it is compared to 2003, and the fact they STILL haven't fixed their stupid memory management scheme (seriously, why is it swapping when I have 32GB of ram and 25GB+ is unused?), I have accepted that I can't use 2003 (or XP) anymore, because it's been phased out, and Windows 7 is the next best thing.
I have no intention of downgrading to 8 or 8.1, I want a functional computer not a glorified smartphone. Windows 9 I reserve judgement on, but if it follows the path set by Windows 8 I will be missing that out too. Hopefully reactos will be usable by then.