Do I need to play XCOM Enemy Unknown before enemy within?

Tags

1. #unless
2. #there
3. #within
4. #progression
5. #unknown
6. #upgrades
7. #change
8. #enemy
9. #basic
10. #types
11. #options
12. #compelling
13. #story
14. #simply
15. #expansion
16. #mission
17. #reason
18. #something
19. #really