Don't expect to have a fun time with single player.
Pros:
+ New enemies
+ Interesting boss battles
+ Creative new weapons
+ Travel to different cities within the United States
+ Interesting level design
Cons:
- Awful graphics; extremely pixle-ated design
- Ally AI seems limited, only fire what attacks them which is almost never.
- All enemies skip attacking your companions and attack Hale; making the game much more repetitive.
Conclusion:
+ Great detail on enemies, ex. spinners
+ Interesting level design on outdoor areas
+ Powerful new weapons
- Indoor areas too vague
- Very little effort in improving graphics
- Obviously your player is the prime target