I'm playing solo and really enjoying it.
I'm not a big FPS guy, so maybe my expectations are lower. I'm playing on the 2nd difficulty level and I've been killed plenty of times (but that might be because I'm not a teenager with hundreds of hours of online shooters)
Server has dropped in and out all day, but that hasn't mattered to me.
The world is stunning, the dynamic weather and day/night cycle are very atmospheric.
The vehicles are a mixed bag. Cars are fine as long as you don't drive flat out - accelerate and coast is the key. Helicopters are very tricky to control.
Biggest issue is the game has crashed 3 times today.
Hopefully Ubisoft will add the things people are asking for - better vehicle controls, first person option, ability to wait for dark, ability to customize appearance and loadout of your team, more options to customise the HUD.