What's your definition of a let down game? Here's the definition from Google.
letdown game (let'doun gam) noun. A game in which a player or team submits a lackluster performance immediately following a previous game in which they either put on a dazzling exhibition or pulled off a dramatic win.
That's exactly what the Bucks had. Do that against Golden State and they'll turn the momentum of the entire series in their favor. It's obvious, when several players have bad games like the Bucks had that it was a let down, not something you'd expect from them too often.
On the positive side, despite the poor play among the Bucks stars, the bench showed they can keep them in games. The back breaker was losing Giannis in OT.