Desolator is a conversion of a relatively obscure Sega coin-op, Halls of Kairos, which involves your character going around a maze-like haunted mansion rescuing little kids who are being held captive there.
I remember having played the coin-op personally and as a conversion this is a good effort. It is the coin-op itself that is a little bland on the gameplay side; unfortunately, this aspect has been ported to the Spectrum conversion as well.
Not bad, but not very exciting either, although this is no fault of the Spectrum version.