The regular refs are light years ahead of the replacement refs, I'm surprised so many feel otherwise. It's not the botched calls happening at the speed of the game - no human can always catch those plays that happen as quickly as they do. They are catching many penalties the replacements were missing or ignoring, because they were uncertain of the rules. The players were becoming out of control wit the replacement refs - they could get away with almost anything.
I personally feel they are a massive.. huge! improvement. I'm glad to have them back. They won't always call things the way you want - they will still miss some stuff, but they are so much better than the travesty the NFL hoisted on the teams earlier in the year.