Medal of Honor Allied Assault: War Chest
I regretted starting Allied Assault on hard difficulty fairly early on but I kept going with it. The quick save option more games had back when this was released is a godsend in this game (the Omaha Beach level!!!) The previous MOH games on the PlayStation are challenging but weren't as difficult. The expansion pack, Breakthrough, is one I played on medium difficulty and was still a tough challenge. This game though, like its predecessors, helped pave the way for the COD series and the realistic war FPS' we see today.
The main problem with some of these levels is that it's trial and error based on not being able to see enemies through bushes, but they can see you. The stealth levels also leave some room for improvement. While it has great music, a lot of the score also seems rehashed from MOH: Underground as well.