Finnish has 16, Estonian 14. Though most inflections can be derived via suffixes from about 4 of them (3 singular, 1 plural), What's probably complicated is when to use the correct form.
Bands that have play:
Nigthwish, Symphony X, Ratt, Tarja Turunen, Within Temptation, Deep Purple, Sonata Artica, Angra, Therion, The Gathering, Carcass