As others have said, there may be a few quirks but honestly my phone is running better than it has before and there are more than a few reasons to update, esp if you have a galaxy gear this is the only way to make it compatible. The unstable network thing I have have seen many times on my phone but honestly I haven't noticed an actual change in the way that my connection truly behaves. I also like the new menu options, quick menu drop down, two finger swipe down option (can now slide one or two fingers for the notification window to get different views), support for high resolution contact pictures just to name a few. I won't say it wasn't with out a few weird gremlins but honestly they were easy to fix and weren't issues, just settings you had to reset.
My vote for you, update.