I was there earlier in October for 5 days. Excellent for history, exploring. Can't really comment on nature, but it's highly recommended for snorkelling & scuba, so perhaps there's a lot to see underwater. The weather was great, very warm but with a constant breeze.
Is it dull? To live there, it probably would become dull fairly quickly, if you like change and innovation. It is very small; very Catholic; I had the sense that attitudes change very slowly and tradition is valued; it might be rather parochial compared to other countries. But it's a really good place to visit if you like history, and there seemed to be plenty of cultural activities on offer in Valletta.
We stayed in an AirBNB in Birgu (aka Victoriosa) which was ideal - old, pretty, small, and you just hop on a ferry or a little water taxi across to Valletta.
The prehistoric sites and the Archaeological Museum are excellent.
The architecture and general atmosphere of Mdina, Rabat and Birgu is wonderful, and there are old mansions to visit with antique furniture etc. The Inquisitor's Palace in Birgu was fascinating, not least because the displays tried so hard to minimise and normalise the darkest aspects of what actually went on (eg torture was "only ever carried out for a maximum of 30 minutes at a time" and they supposedly always had a doctor on standby ?!). Valletta is also very beautiful architecturally, but we found it a bit too busy with cruise groups.
We stayed away from the resort areas, focused on the South of the island, and didn't bother with swimming, as the water was too choppy.
There were vegetarian options on every menu, but specifically vegan choices might be a bit harder to find, although Google shows lots of results. I had an amazing vegan pumpkin ravioli with walnuts in a Valletta restaurant near the Food Market (which is actually just a food court with a large Spar in the basement). The nicest place for eating was waterside in Senglea.