Two Questions: I Have Been On Toprol-XL 50 Mg. For

Two questions: I have been on Toprol-XL 50 mg. for 10 years. My Medicare Part D plan has informed me that starting Jan. 1, 2017, it will no longer cover this drug. It is the only prescription drug I take. It recommended replacing it with Metoprolol ER. Is this the generic form? I had tried a generic a couple years ago, but it wasn't satisfactory so my Dr. switched me back to Toprol-XL. What could be the difference in the two drugs besides price? Thank you.