I agree with the second post. Like many great elegies (such as "Lycidas," by John Milton, or the "Anniversary" poems of John Donne), this poem does much more than simply memorialize a dead person. It becomes an opportunity for Tennyson to meditate on a wide variety of important issues, including matters of religious faith. The fact that the poem is so very long almost guarantees that it will do more than pay tribute to the dead friend. The poem was very strongly admired in the Victorian period, including by Queen Victoria herself.
He does up to a certain point. Let us remember that, while this incredible poem is written as a pageant to his dead friend, Hallam, Tennyson also uses this poem to explore his own faith struggles and how contemporary science had created a conflict between traditional religious belief and the new discoveries that science was unveiling. Therefore it would be wrong to read this poem as just an elegaic remembrance of a dead person as it is so much more than that.