Got it early on Xbox One. 20gb install (surprisingly small). Played 90 minutes. To be honest - a bit meh so far. It felt like lots of chores combined with Assassin's Creed mated with Splinter Cell for stealthy bits.
Graphically, I compared playing with some MP4 versions of PC gameplay and I'd say it's about 'High' from PC. During the daytime the game looks.. really bland most of the time. There's some good weather effects - fog actually looks good, and when it rains you get puddles that pool well (i.e. it looks realistic). Open water looks great, reminds me of those Skyrim water mods people made.
If I'm completely honest I'd say the difference between driving around in GTA 5 for the first time, watching the sun set (on an 8 year console) and driving around in Watch Dogs for the first time is interesting. I had feelings during GTA 5, and remember thinking "Wow, this is amazing". Played the first big 'next gen' game and ended up order take out instead.