It seems like anyone that's talked to me this year has heard me going on and on about how Power Query is just the nicest new bit of tech that's come from Microsoft lately. We cover it as part of our one-day Power BI Core Skills training class and as part of day 2 in our BI Core Skills classes that we recently updated for SQL Server 2014. Out of all the technologies that people see during that week, Power Query is the one that seems to promote the biggest discussions.
It's also a product that keeps getting improved constantly. Another new update for Power Query is out and you can find it here: http://www.microsoft.com/en-us/download/details.aspx?id=39379&WT.mc_id=Blog_PBI_Announce_DI
Here is a video that shows what's been updated: https://www.youtube.com/watch?v=Q9boOzu298Q
The blog post from the team that shows what's changed is here: http://blogs.msdn.com/b/powerbi/archive/2014/06/26/6-new-updates-in-power-query-june-2014.aspx
For me, the one big thing that Power Query is now missing is a corporate story beyond Excel/Power BI. The queries that you create in Power Query are actually M language queries. This is a very capable language (unrelated to what the industry used to call the M language), that Microsoft have documented here: http://go.microsoft.com/fwlink/?LinkID=320633
I would so love to be able to take the queries that I generate in Excel and paste them into an SSIS data source, or use them as a data source in SSAS tabular. Once those types of options appear (surely they must), this is going to be even more of a killer application.