Epic Meepo
Hero
I'd say Arcadia is very alien. The sun is a rotating, hemispherical spotlight that never sets, and rivers inexplicably make perfect 90-degree turns. Plus, it's the only Outer Plane that's being slowly devoured by one of its neighbors, as hives of ant-people slowly drag it into Mechanus from below.I actually love most of them just about equally. But... there are a few that I really don't like. It's simply a matter that if you're in an Outer Plane, it has to feel unworldly. Basically a "we're not on the Material Plane any more, Toto!" situation when you get your bearings and look around. In most cases, this would be instantaneous, but even those that take a few moments for your mind to be blown ("There's land above us where the sky should be!", "The sun/moon isn't rising or setting!", "There's a huge mountain over there with a torus floating above it!") are still good. It's the ones like Arcadia and Elysium, which would be hard to differentiate from Material Plane worlds which are the ones I don't like much. Yes, Elysium has its secrets and trapping mechanism, but that's nowhere immediately apparent, and all Arcadia has is its Storm Kings, something that someone from a deity- and magic-filled Material world wouldn't consider terribly outlandish...
I do think your critique of Elysium is spot-on. It's just not that visually distinct. (Despite that, I'm fond of the way travel works on that plane: as long as you have no interest in performing good deeds, you never reach your destination. It's the most humane defense mechanism of any Upper Plane. An army of demons could invade, and they'd just get lost in the wilderness for the rest of eternity.)