That area is complete enough to fulfill your quest there
Axis3123, with the additional bonus that it is now a good place to find purple herbs. After you beat the boss of the marsh area there is a cave to explore with its own boss. Text regarding "turning back" after beating the marsh boss seems to imply the marsh will be expanded further, but it could also just be a player hint to prevent them from wasting time in the swamp.
One of the rewards you get from the previous quest before the swamp should be boots that enable you to walk over dangerous tiles without getting hurt or slowed. If you managed to multi-class a Dark Soldier build to blast enemies with magic it will be useful here. When it was my time to clear this area I took a solo character with the boots and swiftly flew through the area by skipping non-critical fights and using a fire spell that hits all enemies at once to attack the vines and flower.
That said after exploring the area felt a bit pointless. Maybe the swamp will be expanded upon. The purple herbs give some reason to come back. I suppose part of the pointlessness is the lack of sexy enemies and prizes there. The entire area mostly feels like a lock to pick to access the cave area for its boss. I blame the unfun of poison and movement slowing mechanics. It's the modern-day water level of gaming today, which in the previous gaming generation was the most complained about kind of level. They have qualities in common; swimming or walking through mud slows you down a lot, and these areas tend to be maze-like. You can blame LoZ Water Temple for the water level stereotype, and DS Blighttown for the swamp stereotype.