Personally I think Steam is one of the best game platform (for a lack of a better word). It is fast, easy to use, nice sales/cheap in general, downloads are quick. While on the other side Playstation store is the exact oposite of what I just wrote.
my main complaint is that I find it pretty clunky and slow.
edit: The UI, not downloads. Browsing the store is usually not that pleasant, switching tabs, etc... Downloads usually cap out around 40MB/sec on my connection. Which is fine.
Desura, UPlay, etc. seem to have little to no comparability in options, versatility and ease of use.
I remember when Steam WAS really horrible. The green client ran so poorly and was extremely slow at updating anything,
I feel like we're using different clients. My steam client is slow, clunky and often gets in the way of games. Yes, the sales are cheap, and the downloads are quick, but that's irrelevant to the client.
Finally, the vast majority of time in the gaming experience is not spent in the store. It's all about the content and the exclusives. Sony has invested heavily here.