Office 2016
Word and Excel are draining the battery, even if they can handle App Nap. I was on a 10h flight last month with my MBPr 15 and I started writing a document in Word. The battery status indicated 3.5h left, at 100% charge. I promptly switched to Pages and TextEdit and I got 10 hours of battery left. The same is happening with the rMB. From 2.5 hours to 3.5 hours with 100% battery and Word/Excel open.
Current version does not work great unfortunately. There are A LOT of bugs, especially with double screen or when full screen. You are right that it is a significant improvement over the crappy 2011, but we are way beyond the Windows version. Running Excel on Parallels is a better experience than the native 2016 for Mac.
The second problematic app is also Box Sync. It consumes 20% of CPU every time is syncing, and if you are working on the cloud, this means that 20% of CPU is always occupied by the app.