The BBC & the CBC produce a lot of dramatic radio with full casts & music & sound effects, but not all that much science fiction - see BBC Radio 4 Extra, for example. CBC’s Vanishing Point is the most recent dedicated speculative fiction show I’m aware of with that level of production values.
There have actually been a lot of really good independent audio dramas in recent years. To name just a few:
Edict Zero - A police procedural on a far flung colony planet.
Orphans - A group of people with no memory crash land on a mysterious planet where they're being hunted.
Archive 81 - Starts as a story about a guy investigating paranormal tapes, then eventually moves into more of a dark fantasy type setting.
Theater of Tomorrow: A SciFi anthology series, with some relatively long multi-part stories.
StarTripper!! - Lighthearted show about a desk clerk in the future who grows bored of his day job and buys a spaceship to travel around the galaxy.
Our Fair City - Set in a futuristic city standing alone in a post apocalyptic wasteland, it's a bit of a screwball comedy/drama dealing with the various residents who reside there.
MarsCorp - SciFi comedy about a woman who's been reassigned to assist the Martian colony effort and finds the entire project on the verge of collapse.
As you can probably tell, I tend to listen to shows in the SciFi/Fantasy genre. There's a lot out there, but I picked ones that are relatively well written (in my opinion) and give the feeling of a big production (full cast and sound effects).
