Hey Badger

Marshes:
Overall looks pretty good, would only suggest
- Play around with more height differences, you can easily stack these plants up to achieve many different heights
- Maybe try to organize your veg a bit more, eg. have reeds closest to the water, dryer plants on places far away from water, more plants in groups/clumps ...

Tom Bombadil:
I really like the shape of it!
- The spruce wood texture on your house is not a pretty sight, I'd avoid using it right now, could use jungle or maybe some planks (as I assume you don't want it oak like the tree)
- The interior feels much less alive, maybe having the tree or nature in general also incorporated on the inside would be nice.

Umbar:
Also nice ideas and shapes
- The red bricks stand out too much when used on the path
- Would have used a different colour than the dark blue for the houses, the light blue would seem more appropriate seeing the level of decay of the houses.
- Streets feel empty, add cars, stalls, crates, outdoor workshops, construction scaffolding?...

Dale:
- The houses look boring and lack interesting elements. Could have added some more colours to them, like white bricks, maybe some stucco, the brown pillars... (look at movie version for example)
- The trees look quite nice, but out of place, maybe due to it not being finished though. Also would expect more pine like trees in Dale.
- Add way more vegetation to your ground, mainly grass, but pretty much every grass block should be filled with something
- Make your roads a different colour than your houses, probably some grey bricks or a dirt path instead of additional sandstone.
- Use more than 1 colour of shingles.

Overall you seem to have the right ideas, though still need some practice to bring them nicely into Minecraft. That'll get better over time I reckon.

Update, added:

@aVeryAngryBadger very kindly asked me to take a screenshot of herself decorating the interior of her house.