The dialectic method encourages us to question our claims and the ground on which we make our claims. Socrates' cross-examination digs up the assumptions and the reasoning that underlie certain claims and exposes them to scrutiny. It emphasizes careful reasoning, logical thinking, and the necessity of reaching agreement at each stage of the dialectic. It is no wonder, then, that Socrates is mistrustful of the carefully crafted rhetoric that he has seen already. Poetic turns of phrase and the like are, to him, simply means of covering up shoddy reasoning and unwarranted assumptions. This sentiment is strongly justified in Agathon's speech, whose rhetorical flourishes do their best to protect what are very clearly some unsupported and grandiose claims.
Socrates opens with the remark that he cannot speak well if speaking well means forming well-crafted sentences, but that he can speak the plain truth. This remark echoes the opening of the Apology, where Socrates similarly mocks his opponents' careful rhetoric and prepares the audience for his simple speech. In both cases, we might ask to what extent Socrates is feigning naivete. Plato is a formidable writer, and the style of Socrates' speech, while not marked by the techniques of the orators (though it is occasionally in the Apology), certainly betrays a high level of careful crafting.
The philosophical move made in this passage is to suggest that Love is primarily a relational property that holds between things. That is, Love is not itself beautiful or good or anything else so much as it is a relation that holds between the beautiful, the good, and those who love. This claim will be brought out more explicitly in later passages, but we should give it some examination now. In particular, Socrates/Plato may be right in identifying Love as a relation, but there is no support given for defining it as the particular type of relation Socrates/Plato describe; that is, Socrates statement that Love is love of something, a relation between lover and object of desire. Love could equally well be a relation that exists between two people or between two kinds of behavior or all sorts of other things. There is only superficial justification for the particular choice of relation.
Further, the reasoning near the end, where Socrates claims to show that Love wholly lacks beauty, is questionable on two counts. First, one can desire beauty without oneself being ugly. Socrates here seems to be fudging the distinction between love or desire for concrete objects and love or desire of abstract ideas, like beauty. I can't want to have a car if I already have a car, but I can want to have beautiful things and still be beautiful myself. Second, Socrates leaps from the claim that Love's desire for beauty suggests that it lacks beauty to the claim that Love is wholly without beauty. Couldn't Love be somewhat beautiful and desire to be even more beautiful? There is also an ambiguity in the language of this passage, where it is unclear whether Socrates is speaking of Love itself or of a person who loves.