Perhaps this falls more in the "famous" camp than the definition of "underrated" requires, but I still don't think it's beloved like it should be. We pick up where the Season 4 finale left us, with Ross saying he takes "thee Rachel", we move through Monica and Chandler attempting to secretly hook up, Ross searching for a runaway Emily, Rachel loving Ross, and Joey perfectly appearing when the story needs him, all the way to an ending of Rachel flying to Greece alone on Ross and Emily's honeymoon. It's 22-minutes of clever, quick chaos. (Note: at one point Emily hits Ross, and that's not okay.)
Monica: "You didn't find her?"
Ross: "No. I've looked everywhere."
Chandler: "Well you couldn't have looked everywhere or else you would've found her."
Monica: "Yeah, I think you should keep looking."
Chandler: "Yeah, for about, uh, 30 minutes?"
Monica: "Or 45."
Chandler: "Wow, in 45 minutes you could find her twice."