So I know it is a bit late but I just got my alpha today. My thoughts on this new client are great. The design is really good and easy to use. However the things that were a bit worrying to me were that on mediocore laptops/ PC's the animations may take too long. An example was when I was in the banning phase of the draft mode it took about 5-7 seconds just for the animation to finish and the champions to pop up. We know that there are cases where players have 30 seconds to ban a champion and still fail to do so within that time window. During the skin picking I also noticed that the splash for a skin slows down the process as it's pretty much full screen. It looks really nice don't get me wrong I really loved it but it made my client a bit slower. Overall I think that the client is really great it gives a whole fresh feeling to the game and I have really good hopes for the final outcome of the new client. I will continue to try out the client and try to see any other problems with it.
PS. I forgot to mention that there were times where I had an invite from my friend to play a game and the notification did not show up and when I went back to the old client it worked as normal. That's all that I have noticed so far with the client.