Power Query and Power Pivot are the most valuable features. You can easily manage your data on Excel. İf you have a professional version, you can do it. However, if you don't use Power Query and Power Pivot, then your raw number is limited. The Unpivot specialty is useful because you can't do it in the front-side of Excel.
Improvements to My Organization
If you don't have any analytical tool and you don't have any budget, then Power BI can be the best product in terms of the price-quality index. This is because you can work easily on big data; you can upload and model it.
Room for Improvement
Performance can be better; of course, it depends on your hardware but it can also be improved.
Once I tried to upload 5 million rows on Power Query from a CSV file but I got an error about my personal computer, i.e., my RAM was not enough for uploading. Also, sometimes this process takes a long time.
Use of Solution
I have used this solution for about three years.
There were no stability issues.
Customer Service and Technical Support
Once I asked a question to the technical support team and they answered clearly. I would give them a 9/10 rating.
It is a user-friendly tool, but the data size is important, i.e., you have to check your data size and how you can use it effectively.
Disclosure: I am a real user, and this review is based on my own experience and opinions.