Don is a very good announcer. As others have noted, he allows Remy and Eck to lead the way in terms of broadcast personality, but he's an excellent straight man. And frankly I think he's been even better on the TBS playoff broadcasts he's done, because he's working with an unfamiliar crew and not covering the Sox, and thus seems to take the lead a little bit more and be more of a director about the action on the field. He doesn't overtalk, thank God, and while he's obviously a homer he's nowhere near the insufferable acts we've seen other teams' broadcasters pull.
There's only one Vin Scully. Harry Kalas is dead. This talk about needing a top 5 announcer seems to ignore who the other guys around the league are. The Yankees use the horrible Michael Kay, and they're the best-known team in the universe.
Don is a good broadcaster and it would be a shame if we lost him due to a contract issue.