METS was originally created as a wonky and complicated set of Drupal 7 pages with lots of bespoke hardcoded HTML, like what you are seeing, but along with working with Cast Iron Coding to migrate METS to a modern web application stack (https://castironcoding.com/article/mets-case-study) the team behind METS is also now working to transform all the fiddly HTML into much more feature-rich TEI-XML (https://tei-c.org/). You can already see the differences in features when filtering on the Editions page by the "TEI-XML" category, which is eventually how all the texts will look and operate (https://metseditions.org/editions?time_period=&category%5B%5...). A lot of that transformation can be automated luckily, but there are editors that are going to be doing the remaining work to get the transformation done.
Also, FWIW, the staff behind METS was funded by an NEH grant that was recently cancelled. The folks behind the publication series are now very much in fundraising mode to try and make up the extreme shortfall, so if anyone is interested in helping keeping this open and free resource online, donations very welcome!
I'm charmed by the Middle English footnoting style of providing glosses for words that may trouble the modern-English-speaking reader without bothering to note which words those glosses are for.
However, this edition isn't typeset correctly, and the glosses are appearing attached to the wrong lines. (At least, I'm assuming that "great", glossing an empty line, is meant to gloss "grete" on the following line, and "shameful deeds", on the line "And the precious prayer / of his pris Moder" is actually meant to gloss the following line "Sheld us fro shamesdeede / and sinful workes".)†
This is a pretty serious problem.
More generally, these appear to be edited critical editions, and I wish academic texts would actually display the text of the work they represent. I don't mind displaying a standardized "editor's rendering", but show the actual text too. I want to know what the scribe wrote. This is an electronic reference. We can afford the space.
† Tangentially, it's also interesting that "sinful" counts as alliterating with "shield" and "shame".