While us wargamers and historians know and recognise 'Les Grognards', many will not and won't have a clue what it means or what a game given that title will include. remember we want this game to sell to a wide audience, not just the hard core wargaming audience.
I would suggest a title with 'Napoleon' in it, then the subject matter is no longer in doubt.
How about 'Napoleon's Wars' or 'Napoleon, Empire and War', or 'The Campaigns of Napoleon' or something that summarises both the subject matter and game content.