I am not that far in, I just got this game last week and have been trying to finish Professor Clayton before I focus on Contra 4.
In the brief time I have spent with C4 I can say that it is truly challenging, even more so than the old school arcade and NES & SNES Contra games. This game would bring most of todays "Hardcore Gamers" to tears. I loved the levels I've played through, sounds like boss 6 is gonna be a pain in my @55!
If you like challenging games, pick this up! Konami really delivered both fan service and true old school difficulty with this one!
Wii Code 3456 7941 4060 2924