Filter Views (collaborative work), zoom and freeze panes
As much as I love using Excel Desktop version, online version is not that easy to use.
Few ideas (for on-line I prefer using google only because it have features very easy to use):
1. Filter Views - addressing the need of multiple people working in the same time, in the same spreadsheet but each on it's own view without bothering other folks
Freeze panes - would be easier just to "drag" a line (as is with Google) and freeze whatever rows, columns etc.
Rearrange the order of the column and rows - again referring to Google Drive where it's so easy to select a row and a column (drag and drop 1second action)