Batalha Monastery is a masterpiece of Gothic and Manueline art. I visited all three WH monastic complexes in the Centro Region of Portugal in April of 2019, and the contrast between Alcobaça and Batalha, specifically, is one of the strongest impressions of seeing these places. Where the cloisters at Alcobaça are restrained, the ones in Batalha are outright exuberant.
There are three main impressive components to the Batalha site, starting with the Founders’ Chapel, the first royal pantheon of Portugal. The square-plan chapel is unexpectedly bright for what is technically a crypt, including vivid stained glass. Next are the cloisters of King João I, intricately decorated throughout. The decorative details range from very complex to sometimes simple, but all are just delightful to explore. A small detraction from the overall impression are the black stains on the yellow stones. Again contrasting this with Alcobaça, the monastery there appears very thoroughly cared for, whereas Batalha feels not exactly neglected but also not really in the best shape it could be.
The last component of the complex are the Unfinished Chapels. The principal work on the monastery construction continued into the 16th century (having been started in 1386), but the adjoining yet separate octagonal structure of the Capelas Imperfeitas was never fully built. It is the killer feature of the monastery, resplendently decorated with lacework of Manueline motives.
Most of the visitors will likely come to Batalha from Lisbon, which should take about an hour and a half by car (about the same time as between Lisbon and Alcobaça; you need about half an hour to get from one to another). The sufficient time to see the monastery is between an hour and an hour and a half. The surrounding town feels fairly lively but without significant points of interest beyond the monastery.