Hi Chris.
While you
can downgrade, I don't know that I would recommend it. First, even if you do get back to Kitkat, you will continue to get notices about the update to 5.0 to the point of irritation. It is a Nexus after all and is supposed to be on the latest version. Next, 5.0 really is better. It is a bit of a change (okay, it's a MAJOR change) but give it a chance, if you have a Nexus, I bet you'll grow to love it. If you are adamant about downgrading (your phone, your choice) here's the quick list ...
1. Get the
Android SDK, Google drivers and Java Development Platform. Install them.
2. Get the 4.4.4 factory image from Google.
4.4.4 (KTU84P) and decompress the contents into the platform-tools folder of the SDK.
3. Put your phone into fastboot mode (with phone off, power + vol. down buttons).
4. Plug in phone and let drivers install, if they aren't already. Test this by opening an elevated command window (Start menu, type "cmd" in search. When you see cmd.exe right click and select run as administrator) then change directory to platform-tools. Type "fastboot devices" (no quotes) and you should see a serial number listed. If you do, then ...
5. Run Flash-all.bat
Let it do it's thing. You phone will reboot a bunch and it can take a while. Remember it's replacing pretty much everything on your phone. (BACKUP FIRST OR IT'S GONE!!!)
Yourlag and crashes are most likely from the OTA. A factory reset now will most likely clear that, but backup first. We see this all the time with every version upgrade. From 2.1 to 2.2 ... to 2.3 ... to 4.0, etc. These major changes work well for most, but there's always a group that get's into trouble. 99% of the time a factor reset cleans things up, and they come back singing the praises of the update once it's working correctly.
If you want a perfectly clean install of 5.0 (lollipop) just follow the instructions above, but use the 5.0 factory image files. Everything else is the same.