First, we have two episodes dedicated to the sensational British boys-band The Beatles: 5x1: Love, Love, Love ; and 5x2: Tina In The Sky With Diamonds.
Also, we know that the cast put up together a tribute episode in memory of their late co-star Cory Monteith. The third episode of the season, Forever Finn, will air on the 10th of October.
Then, we've heard about the "Klaine" (Kurt + Blaine) wedding. The fans are really excited about it, because the couple had a serious break-up in the 4th season so it's great news to have them back together.
On a saddest note, we learned that Jayma Mays, who plays Emma Pilsbury, is leaving Glee to start acting in a new series.
However - and that's great news - we know that one of the 5th season's guest stars is famous Demi Lovato. Apparently, her character is going to be a singer in NY and Santana Lopez' girlfriend.
To sum up, I think it's going to be a GREAT season, even though we're going to miss Cory a lot, and it's kind of weird not having Finn out there.