הלכה על שבת 303:1

And that which they said there that the one who is completely righteous in judgement is sealed immediately for life in the World To Come. Do not think that the World To Come is something that is identical for all righteous people; for in that life there are countless gradations, and each righteous person rises to the fitting level according to his reward (See Shabbat 152a). And the rest of the details about these matters are there in the first chapter of Rosh Hashanah (see Tur, Orach Chaim 602-603).