I love spy missions. They're my favorite.
Of course re-discovering them after a long while provides even more enjoyment.
The Lua one is one of the funniest of the bunch, you have puzzles, parkour, races, time attacks and Danger.
Edit: I realised kinda late that the run I did on Lich Territory most ilkely removed all presence of Corpus. Making it both easier at times and harder at others.
It's still possible to do it without being on Lich Territory but just to be clear I goofed that