Nexus 5- no improvement over Nexus 4 
EDIT: Received RMA Unit this morning, very fast replacement from Google. Display, Heat and battery life issues are all gone I assume I really did get a bad unit...
Washed out still compared to other 1080p panels on the market, poor viewing angles again same issues as Nexus 4
About 1hr 30- 2hr 10min screen on time sometimes more sometimes less inconsistent, exactly the same as Nexus 4, standby times seem worse.
Testing battery on new unit....
Moto X 2200mah
-dual core 1.7Ghz,4.7in 720p display
Nexus 5 2300mah
-Quad core 2.3Ghz,5in 1080p display
I guess Google engineers were able to agree that 100mah more than the Moto X will be enough for 2 additional cores a 1080p display +.3in in display size and a max CPU speed 800Mhz more than the X as well as a more power hungry GPU.
a lot the longer you run a heavy application just like Nexus 4. Google hasnt improved how the phone cools itself at all with the Nexus 4 it had an air gap between the chassis and processor not allowing heat to pass through. These issues are a lot less dramatic on the LG G2 or Moto X. Same exact issues on Nexus 4
"Nexus 5 at 63°C, initially dropping to 1958 MHz (from 2265 MHz maximum) , then as temperature continued to rise up to maximum of 69°C it throttled further, 1728 MHz, and eventually dropping CPU to 1036 MHz."
Bad just like Nexus 4, only difference is instead of it being on the back its not on the side! no quality improvement at all
The only complete improvement over the Nexus 4, update has helped still work to be done but its getting better.
Overall this phone is not well rounded, powerful but lacking in
many areas to keep the price low. What google should do is release a Nexus at a higher price with high end hardware everywhere. They are not taking the Nexus phone program as seriously as they should and its hurting the Nexus name.