>>105659957 (OP)- a few disastrous day zero bugs, like file copying being broken (well, it worked, but sometimes dropped to 10kb/s even on sequential transfers)
- paradigm change in how app security is handled resulting in all existing applications throwing you UAC prompts. this was a good thing, but end users only saw it as an annoyance because every app to this point was made with the assumptions that you are running as admin.
but the worst part was that
- hardware vendors released broken or no drivers, even for hardware that could run the OS fine (I've seen dozens of nForce3 setups where absolute high end systems got stuck at XP), or worse, new hardware that was meant to take advantage of Vista (nvidia 8800, a DX10 card, didn't get Vista drivers until later).
- OEMs plastered the "Vista Ready" sticker on low-end shitboxes that could, at most, barely boot Vista and run it in the most basic mode.
Three years later, we had enough hardware with compatible drivers, and app devs updated everything to run in user space, so Win7 had no such problems at launch. But I guarantee you, if Win7 had launched in 2006 into the same environment as Vista, it would've been just as disastrous.