A few effects off the top of my head:
Sky Coloration
A thicker atmosphere favors higher frequencies of the sky at midday and lower frequencies at sunset due to Rayleigh scattering. If your planet orbits a boring old G-type main-sequence star like our sun, its sky will likely be a dim violet, as the dominant frequency should be somewhere in the ultraviolet, and at sunset, it should be dim red or black.
If your planet orbits a red dwarf, on the other hand, the sky could be orange, yellow or even green at midday (still red at sunset) depending on things like the amount of dust in the atmosphere (that causes a separate process called Mie scattering, which is why Mars's sky is yellow). No matter what, there won't be a lot of light reaching the surface (though probably still more than how much reaches the Earth at night), but anything that evolved there will be used to that.
Climate
High pressure at the surface makes it much harder for surface water to evaporate, so your planet will tend to be drier than Earth. That said, climate is incredibly complicated and full of feedback loops, so far instance if you have a large forest biome, the water exhaled by the plants could still result in rain on its own.
Since your planet has a high cloud layer and high atmospheric drag, rain will take a long time to reach the surface, and indeed will likely evaporate and condense multiple times before touching land. This means that rain falls far from where it evaporated, which I think will make your planet more ecologically homogeneous. Fewer sharp boundaries between forest and desert; every ecosystem will be larger and more blurred together with its neighbors.
Visibility
Also due to Rayleigh scattering, a thicker atmosphere makes faraway things harder to see, since the light that reflects off of them gets scattered. It's a negligible effect on Earth, most noticeable when looking at mountains near the horizon (they kind of seem to fade into the sky). But on your planet, it will be much more significant, not just because there's more atmosphere, but because everyone's flying.
The distance to the horizon is pretty much directly proportional to your height, which means flying things can potentially see a lot farther. I'd expect them to hit this visibility limit way more frequently than we do on Earth, to the extent that the horizon usually won't be visible unless they're very close to the ground. Instead, the ground will gradually fade away like there's a thin, blue-violet fog.