• papuḥ — they drank
  The verb is from pā — to drink. Bhāgavata aesthetics: darśana is anna for the eye; Kṛṣṇa-rūpa is the soul's nectar. Compare SB 10.13 (the calves and boys whose eyes drank Kṛṣṇa for a year).
• na-tṛptāḥ — not satiated
  The Gauḍīya cornerstone phrase — Caitanya-caritāmṛta Madhya 21 quotes this exact pattern to define mahābhāva. With ordinary objects, increase decreases desire; with Kṛṣṇa, increase increases desire. This is Bhāgavata-rasa's signature asymmetry. A contiguous-token join of synonyms 'na' and 'tṛptāḥ'.
• uttama-pūruṣau — the Supreme Personalities
  Dual — both Bhagavān and Balarāma are 'uttama-puruṣa'. The Gītā's 15th chapter defines uttama-puruṣa as Bhagavān above kṣara and akṣara; the Bhāgavatam extends the title naturally to Balarāma-tattva. A contiguous-token join of synonyms 'uttama' and 'pūruṣau'.
• praharṣa — of their joy
  Praharṣa is the burst of sāttvika happiness — one of the eight sthāyibhāvas' anubhāvas in Rūpa Gosvāmī's analysis. The verse documents it: eyes widen, faces flower, the whole body becomes a register of darśana-ānanda.

The people of Mathurā drink Bhagavān with their eyes and cannot be filled. This is darśana-tṛṣṇā — the thirst that grows the more it drinks. A mundane sight tires the eye; Kṛṣṇa's form expands it, opens it wider, refuses to satiate. Bhāgavatam's working definition of mādhurya: na tṛptāḥ — never enough.