well, i'd recommend you the two last albums...
"last fair deal gone down"
and
"viva emptiness"
u can find very good examples of what these guys are capable of.
last fair deal gone down is a very sad and mellow album, full of hopeless feelings, loneliness, fear, indifference, love, life and death...personally i love that album.
viva emptiness, on the other side, it's a twisted, dark and agressive album. hate, anger, despair, death, lies, confusion, regret are the feelings around the songs. i like this album very much too.
this would be the ying yang of the latest katatonia productions.
of course there's the old katatonia style, where albums like "brave murder day" and "sounds of decay"
are must-hear metal masterpieces.