I disagree. I've pre-ordered various games that I've been quite confident will be excellent, and haven't regretted it. Often it's a great way of getting the game cheap too, rather than having to wait for a price-drop weeks afterwards.
Same here. Research some information and you are very unlikely to go wrong. So long as you don't base your purchase on just one video or something, you should be fine.
AS I said earlier though, I'm not gonna bother with Watch Dogs. It will just be the same as AC4, totally limiting in every way, all scripted actions with an awful UI and running around a mini-map collecting icons.