I just installed 1.5.1 (x64) today and as someone else reported, I had to re-add all of my custom URL cameras; however, no big deal.
My first issue is a major change was made in the way we view thumbs in the library. The way it used to be was that it scrolled horizontally and wrapped each line with the mouse scroll button. This was great for going through hundreds of thumbnails looking for anything of interest. I often get hundreds of thumbnails per day on my outdoor cameras from rain/snow/fog/spiders/etc. and this scrolling method allowed me to stare at a single thumb on the screen and scroll through them all, easily identifying anything of interest. Now, I have to scan the row manually across which is not only much harder to do, it is much less accurate at picking out small differences.
My next issue is not new in this version, but still persists. If I am in the library view and view a couple of clips, everything is fine. However, if I get distracted by an incoming email of whatever, and go back a few minutes later to look at more clips, the authentication to the server has timed out. The timer is too short, and in my opinion, shouldn’t be there at all. I have to log out and back in to resume watching clips. Also, in this version, you are not even prompted to reauthenticate as in the previous version.