The problem I usually met with Windows store is that compared to Google play store or Apple app store, the connection is always slow and not as stable as the other platforms like M$ couldn't afford a good server providing quality service.
I'm sick of seeing those try again errors pop for no reason while my other IMs, WebPages, dropbox, teamviewer are working smoothly and this issue is not only exist within w10m, my w10 devices are also suffer from time to time....
I agree it is rather slow, I have a fibre connection and even on that it can be diabolically slow at times. As after an update it would become ridiculously slow and the following updates will fix that and it becomes fast + fluid then the next update will bring back to a slow crawl again.
Instances like that are indicative of stretched resources and coding hours as the developers don't have the time to optimise. Unfortunately as Microsoft has fired their programmatic testers who were also responsible for quality assurances, this behaviour will not end until Microsoft rehires programmatic testers for quality assurance giving the developers much more breathing room.
Relying on developers to reiterate and test for every conceivable instance / flaw its simply not possible.
Unfortunately this "lag" also persists with Skype but then again the Skype experience has been pretty much woeful for years. Windows Live messenger was much more polished, the defunct rooms on windows phone also used the windows live messenger back end and along with the passport.net custom logins there was so much more flexibility but with skype?
Not so much.
I am hoping with Andromeda and Polaris the store experience will become much more polished as that is the only monetisation point for developers.