yea...if you've seen the whole original season, then TSR is incredible. But Fumofuu ties together a few loose ends, so I'd suggest watching that before TSR. But only think about watching it if your parents don't mind a bit of swearing (ep. 7) or censored nudity (ep 8....but it's really really close to not being censored...).
FMP is just a downright good anime
Fumofuu is about school life with the same characters and ties together many loose ends between the original and TSR
TSR ties everything up and manages to bring up the big question: "What do we struggle for in life, and why?". It gets pretty serious, especially the last 5 episodes...I won't spoil anything at all, but watch em all...
http://tv-links.co.uk/Full%20Metal%20Panic_links.html^fumofuu isn't on there, but go ahead and watch those couple and you should be fairly happy...
EDIT: alot of TSR has been removed, so watch as much of the original as you can and i'll reupload the rest of TSR later...