The catacombs in Malta have everything a true catacomb should have: A proud roman/christian origin,an underground labyrinth and a slightly creepy athmosphere. I have visited the St Pauls and the St Agatha catacombs in Rabat. They are in walking distance to Mdina, but can be a bit difficult to find. Especially tricky is the fact that the St Pauls church offers visits to the St Pauls grotto (and catacombs - but not THAT catacombs). In fact, all these catacombs might have been connected in ancient times, and the different names and access methods originate from more modern times. The difference between the St Pauls and St Agatha catacombs is mainly in the operation method. St Pauls catacombs are operated by Heritage Malta and accept the Malta multipass. The tour is self-guided, and you can easily make photos. St Agatha catacombs must be paid extra, and be explored with a tour. The visited area is smaller than St Pauls, and photographs are forbidden. As a plus, St Agatha comes with an underground chapel with very nice frescos. Also, many tombs have the original bones inside of them, adding to the athmosphere.
The visiting experience in both catacombs was quite nice, although there are very few decorations or inscriptions. Compared with the catacombs in Rome, the experience is roughly similar, although the catacombs of Rome are much bigger and more famous.
All in all, the catacombs are one of the stronger entries in Maltas tentative list. The big question is if the catacombs of Rome have already blocked the catacombs-as-WHS niche. If Malta wants to play safe, they could combine the catacomb tentative site with the Mdina tentative site for a really strong contender. At least, they could come up with a less boring name. In any case, I wouldn't be unhappy if Malta's catacombs get on the WHS list.

Visited in April 2019.
Importance 2/5 Beauty 4/5 Uniqueness 3/5 Environment 3/5 Experience 4/5