The new format is actually easy to understand. Instead of having 32 teams in 8 groups, we have a league consisting of 36 teams in it. No groups anymore. The rules are the same with the Champions League new format like @imamusma mentioned the details. I hope it'd be fun. I'm not even sure if there was any need for such format change but anyway we'll see. 
The last champion is Atalanta. It was a really unexpected ending while Leverkusen were destroying every single team ahead of them. For now I'm hopeful about Manchester United this season.
No one can stop the changes because we all understand things are going tougher after every year, and we are having more things to do so UEFA is also working on to increase their revenue so they are increasing the number of matches and teams because this will help them for having things on better way in the future.The last champion is Atalanta. It was a really unexpected ending while Leverkusen were destroying every single team ahead of them. For now I'm hopeful about Manchester United this season.
Ending of relegation through Champions League is surely having some impact but still things will be well, and we will have too many quality clubs will be play here and fans will be also able to watch good soccer as they were having this all in last few years Atlanta done magic and having win of last season from nowhere, so things are always surprising and unpredictable because we are having results like these in history of the UEFA for years.
There is change all the time, and UEFA change to make it better in terms of competition and revenue. More teams and matches might bring about some difficulties but it also allows room for more unexpected or exciting moments during the Champions League. While the absence of relegation may later turn out to influence the dynamics, there will be a chance for quality clubs to make strong performances, just like Atalanta has done. There are always surprises in football, and that is what makes it so interesting for fans.
A change may bring in some uncertainty as to the competitiveness between clubs but at the end of the day, football is about entertainment and uncertainty is what makes it exciting. So, no matter how the format changes, the Champions League will still be a tournament that many people look forward to.