Make sure you read up on Emperor Fran's Josef and Elizabeth to learn their true story, because this series is not it.
That being said, it was a very good TV series, well done and entertaining. If you're a stickler for history it will grate for sure, but hopefully will spur viewers to do some research on these characters and the times, and that would not be a bad thing.
The true story of Sisi is actually far more tragic than this portrayal. She did influence her husband in certain matters, particularly in relation to Hungary but her experience as Empress was nowhere near that depicted in this show. She was beloved by the people but spent little time even living in Vienna, and she herself was assassinated when she was in her 60's.
Also interesting is that the Emperor Franz Josef would later be responsible for setting the wheels in motion that resulted in WWI, after his presumptive heir, Franz Ferdinand and his wife Sophie, were assassinated in Sarajevo by a Serbian.
To me, the true story -or history - is almost always better than what these writers and producers feel they need to conjure up for whatever reasons. That's disappointing.
But it's a good TV series, "based on a true story", with good acting, and beautiful direction in a beautiful country. You'll just have to bear with the alterations of fact, something I'm not fond of watching happen but as I said hopeful folks will be intrigued enough to do some research and find out the true story.
I'd recommend watching it but with those caveats.