In this video, James Rolfe - the "Angry Video Game Nerd" - goes in detail over the original two Contra games before also covering some of the other ones, good and bad, in minor detail.
I thought I'd share this video as I think you may like it. Also, his ending speech about childhood memories is pretty poignant.
Be aware, there is some bad language in this video, but I hope you enjoy it in any case:
https://www.youtube.com/watch?v=-XtToNPFU1E