P4 Looks very good to me... I'm seriously tempted, even though I've only had my P3A for less than 4 months. Don't see collision avoidance system as being anything but a big plus (assuming it works reliably) especially as it covers what's underneath as well as what's in front. Also love the tap fly and active track functionality, again as long as they're reliable. For someone like me who's more into the photo/ video opportunities the UAV offers, rather than wanting to just pit my piloting skills against the elements or other pilots, this is a big step forward.
There are things I'm disappointed weren't (or were barely) addressed, such as fixed landing gear and the paltry flight time, but realistically I think they've crammed a lot of improvements into the P4. I will wait a month or so to get feedback as to how reliable the new sensors / functions are, but if it lives up to the promo I'm just gonna have to get one.