The Web version of Excel does a fairly good job of imitating the desktop version's main features. Promised enhancements in the near future? Proper support for Android tablets and a wider range of keyboard shortcuts.
In a post discussing how features are prioritised for the Web-based versions of Excel, Microsoft offers up a large laundry list of updates that will be added in the near future. The two that jumped out at me were "common keyboard shortcuts" and "Android tablet support". Excel online does already support some often-used shortcuts (such as F2 to edit a cell), but it would be great to have full ribbon access. Enhancing Android performance is also welcome, since we haven't yet seen any Android apps from Microsoft for accessing Office documents.
Here's the full list of upcoming improvements:
Adding and Editing Freeze Panes (they are already viewable) Adding and Editing Comments (they are already viewable) Android Tablet Support Editing Files with VBA Chart Editing Viewing, Moving, and Resizing Shapes Loading XLS files in O365 (already works in SkyDrive) Print to PDF WEBSERVICE Functions Common Keyboard Shortcuts Custom Sort a Range (sort on multiple columns) Insert an Image Hide/Unhide Rows & Columns Reorder Sheets Show Aggregates for the Selected Range in the Statusbar Rename a Spreadsheet from within Web Excel Drag and Drop Cells in a Sheet Protect Sheets from Being Edited by Others Insert and Modify Apps for Office
The post also contains a survey where you can specify which features you'd like to see jump from the desktop version to the web. Realistically, the browser-based release is not going to have total feature parity in the near future -- Office makes too much money -- but it can't hurt to ask.
Excel Web - What's in Our Pipeline and Why? [Excel Web]