G'day
Well, my favourite novel is without question 'The Last of the Wine' by Mary Renault. It does a superb job at telling a story set in an alien culture in the voice of a member of that culture addressing his fellows and without ever descending into 'as-you-know'ing. It isn't a work of fantasy or SF (it is set in Greece 429-402 BC), but it is a glowing example to SF and fantasy writers.
Confined to SF and fantasy I would have to choose one of Jack Vance's novel series: probably the Cadwal Chronicles ('Araminta Station', 'Ecce and old Earth', 'Throy'), but perhaps 'Tschai: Planet of Adventure' ('The City of the Chasch', 'The Servants of the Wankh', 'The Dirdir', 'The Pnume') or 'Lyonesse' ('Suldrun's Garden', 'The Green Pearl', 'Madouc').
Regards,
Agback