I like the simplicity of Datalore, but I think it could improve a bit in terms of usability regarding file browsing. A couple of small things I’ve noticed:
The three little dots in the file browser is very hard to click, because it’s so small. It took me some while until I figured out that I could simply use the right click menu. In some way it’s a feature because it pushed be to find an even easier way, but I guess making the button larger is still a good idea… 
I was very surprised that files with the same name can be in the same folder and workspace. This is not really bad, but quite surprising and led to a confusing situation where a colleague and me were working in different files (with the same name) in a shared workspace. I don’t have a good suggestion here.
It would be great to be able to delete open notebooks from the menu. Usually it feels dangerous to delete notebook from its filename alone (see comment above). Opening and going back is a bit cumbersome, also because it takes long to fire up a new machine for each notebook and only 3 notebooks can run at the same time.
Maybe something like a read-only-viewer would be nice. Not sure how to implement that exactly. But I would like to be able to quickly click through notebooks and read them - no need to start the machine in this case, but seeing a file list and the notebook at the same time, might be helpful here.
The “show in folder” menu entry is something I use really often to switch between notebooks. I think the click on the Datalore logo should bring you to the folder of the current notebook.
I feel like I can’t really predict when links are opened in new windows and when they are opened in the same one (also regarding the publish-notebook-open thingy). That might be better to have it in a predictable way, but can’t easily say how to do that precisely.
I have to admit, some of my troubles might be caused because I’m not using sheets but separate notebooks. Not sure why actually. So I have quite some notebooks and need to have all of them open all the time and copy stuff from one to the other.