One of the best 'open' world games to date, beautiful setting (1940-1960? America) and great story. Not overly long to complete (10-15hours).
Metacritic user score gave it 77/100 but I think the Steam user score is more accurate (100%) ;)
It does, however, give the impression of being an unfinished game in terms of development. There are some details that seem to be missing eg trains :( Hopefully they do an even better job with Mafia III
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Mafia 1 > GTA III series > Mafia 2