As a update for those interested: I just wrapped up the finale of a 10 run "season" with my players. None of us had done any Shadowrun before, and I'd say it was a great success overall. My final finale:
The ACHE was used as the center of a blood magic ritual performed by the Black Lodge. While they thought they were wiping Tir Tairngire off the map with a controlled magical tsunami, it was actually a plot orchestrated by Shedim who had taken over their Black Lodge cell to destroy the entire west coast with supernatural flooding. I added an underground mana line which ran beneath the arcology, combined with the geomancy that would be enabled by rearranging rooms and walls, to justify using the ACHE as the final mission. In the end the ritual was stopped, the master shedim killed, but not before he opened an astral rift to let in more shedim - at which point the Johnson who'd hired the runners showed up with a team of Red Samurai intending to enter the rift on an exploratory mission. One player elected to join them, and the rest flew off in a VTOL plane as the entire floor the ritual was done on was blown apart, entombing the rift so nobody could follow.
Everyone seemed to really like using the ACHE as an anything-goes house of horrors. I had a few bits where the player rolled dice to get a random encounter in the halls of the public housing area, and brought a few of the old Deus drones back as security that was dormant, but woken up by the players' actions. I feel like going into the ACHE gives you a lot of options as a GM, since you have a solid 30 year of technology and arbitrary layouts and security to mess with.
