Sam and Max Episode 6 of Season One, Dark Side of the Moon is a great continuation of the series.  And it's got a really need puzzle solving boss battle that harkens back to the former days of glory for the Adventure game market.

However, this game doesn't really stand on it's own.  It depends heavily on previous chunks of the game being well known to the players, and it's a bit of a letdown on the writing side of things.  It's still great... but it's not the best of the series.