Series where the fifth entry is the best

Current Events

By technicality Metal Gear Solid: Revengenance. It came out in 2013, MGS5 came out in 2018. If we aren't counting that, then MGS: Ground Zeroes instead of 5 (because I can't stand Phantom Pain).

If not that, then WWE Smackdown: Here Comes the Pain (Though I still like 4 more myself).

For television series.... The 100 season 5. Right before the show went into the toilet.