I have the offer of Lollipop upgrade but, due to many problems mentioned on this site, I am holding off, at least for now.
To help level the balance, may I ask what are the specific advantages or improvements with Lollipop?
I wasn't all that excited for Lollipop, but after getting the OTA updates for my Nexus 5s, installing them, and using it, I'm liking Lollipop more than KitKat now. The pros outweigh any cons so far, and no real bugs that I can tell. Maybe just some bit of tweaks left to do for Lollipop.
After updating my Nexus 5s to 5.0, I factory reset them and rerooted them without issue with the updated CF-Auto-Root kit.
I'm not really a fan of the color themes either, but the new transition animations, options, and functionality are nice. Overall, I think the update is well worth it and that most people will see it as an improvement.
In particular, I like the new background app. manager (whatever that's called) and pinning apps to the screen and having a password requirement to get back to the home screen; I use a numerical pattern as my password, and now when booting up the unencrypt entry requirement screen has a number pad, which makes entering in my number pattern much easier; the different user options are pretty nice too to set up a new local account, for example, for my wife so that she has her own home screen to use, et cetera.
After using 5.0 personally, I was pleasantly surprised by it.