If we are going strictly by the GoG library and you are looking for recommendations... Hmm...
Well, since you like Battlefield 4 and Bad Company 2, you don't seem to be into realistic military shooters as much. If you were, I would recommend Rainbow Six! I remember that Rainbow Six 2 (I think) was one of the few 12+ rated games in Germany back in the day that featured shooting, so I played it a bunch, but it was super hard! It is more about coming up with a good tactical approach rather than just mindlessly shooting your way through bad guys.
How about Medal of Honor: Allied Assault: War Chest? That's more of a linear, story-driven shooter!
To actually answer your question, my personal favorite would be the Medal of Honor games.
Post edited December 16, 2015 by Cardskeeper