Is it absolutely necessary to upgrade to 2.0?

I’ve tried 2.0 on several different sites, and it’s created a lot of headaches where there was bliss before. I know there are a lot of changes to 2.0, but I don’t like the ones I see, and I don’t need them.

However, are there any big security fixes in 2.0 that would require an upgrade?

Thanks for any feedback.