How does Tennyson use tone and diction to criticise Ulysses?
Overall, I think the poem more empathizes with Ulysses than criticizes him per se.
He describes himself as an "idle" king. You can read his description of his great love, Penelope, as a agèd wife, as disparaging of her, and the term "matched" as a practical pairing of two diminished people. Rather than portraying his subject positively, and caring for them as a ruler should, he thinks of them as a "savage race" and describes the laws he dispenses as unequal.
The tone of the opening seems bitter, and contempotuous of his kingdom and duties. The tone of the ending is grandious, and one could argue that it is used ironically, portraying Ulysses as delusion, and suggesting that he will not in fact be able to accomplish additional great deeds.