Tooling is what sucks. MonoDevelop F# support is very unreliable. Basic refactoring, like rename, don't work correctly every time and I had to literally do git reset few times, after renaming, as it screw up multiple files.

Also, editor often has visual glitches where letters get corrupted and I have to reopen the file to get it back to normal. Not something I expect from such a long time maintained application. However, it looks like Xamarin Studio 6.0 will be much better.

Alternative is Visual Studio Code with Ionide plugin, but I didn't use that beyond trying it once. Hopefully someone else can comment.

Edit: typos