Feature-wise, Excel probably still has more options, but in terms of ergonomics, Google Sheets is much better. And I'm saying this as someone who has used Excel for 20 years.

Here are a few specific examples:

1. Editing formulas using the keyboard only is a nightmare in Excel. It often randomly throws errors and warnings when I move the cursor around (like typing parentheses or quotes first and then trying to move back to type text inside, etc.) before finishing editing.

2. Conditional formatting in Excel is so non-intuitive that I actively try to avoid it like the plague. Yet, I use it extensively in Google Sheets because it is so easy to create multiple rules there.

3. The whole copy/paste design choice in Excel is, in my opinion, weird. Firstly, there is a distinction between copying a cell and copying text: if you copy an entire cell, you cannot paste it as text in a formula or any other input area. You have to copy from the formula bar of that cell. Even for pure cell copying, the cells have to remain highlighted. If you copy a cell and then unselect it (by pressing Esc or trying to edit any cells), the copied content is lost. I'm sure there are reasons it's designed this way, but it's so irritating, and I never find any benefit.

Google Sheets indeed does everything a common user would expect from a spreadsheet, without having to install anything and fiddle with licenses. This in itself is the killer feature.

For me personally the absolute killer feature is the bidirectional integration with BigQuery, something you won’t get that easily (if at all, correct me if I am wrong) with Excel.

As long time Office user since Windows 3.1 days, Google sheets has a lot of terrain to cover up.

Quattro Pro could easily do all of the sheets stuff but document collaboration, ignoring the fact that sheets is a Web application and Quattro Pro started on MS-DOS.