The Game of the Year Edition includes the full game and 5 DLC packs:
MP Supply Pack Alpha
MP Supply Pack Bravo
MP Supply Pack Charlie
Skirmish Pack
Skirmish Pack 2
Men of War: Vietnam Special Edition
The Special Edition DLC includes 3 multiplayer maps and 5 single player scenarios also playable in co-op (up to 4 players)
Men of War Men of War: Condemned Heroes Men of War: Red Tide
Price Comparisons:
Men of War: Assault Squad - Game of the Year Edition [amazon.com] $40
Men of War: Vietnam - Special Edition [amazon.com] $40
Men of War [amazon.com] $15
Men of War: Condemned Heroes [amazon.com] $10
Men of War Red Tide [amazon.com] $25
It seems pretty secure. I used PayPal to buy my copy of the collection and once I was was done paying I was directed to a new page where I was given the Steam activation codes for the games.