It's indeed a lot like powershell, but I found it to be much less painful to use for everyday tasks. I can't really put my finger on it, but powershell always felt very clunky and unpredictable to use. With Nushell, I can write pipelines that usually have the desired behavior on the first try. Also, its more convenient in so many different aspects that I can't go back anymore.
The biggest downside is, that it hasn't had a stable release yet. While I haven't encountered any bugs yet, there are often breaking changes with new releases that may break your scripts.
Take a look at the comments, they explain the issues very well