See also my tasting notes on the 1997s.
The 1998 vintage in Montalcino is sandwiched between two much better years for Brunello. August in particular was so hot and dry that the wines shut down, blocking veraison and the ripening process. Then there was rain at the end of September and in early October so that many of the wines lack a solid core of fruit.
For future reference, 2001 is likely to produce the best wines between 1999 and 2003 while 2002 was very difficult and 2000 not bad.
As these notes on the regular 1998s rather than the...