Hired Guns! It was like Dungeon Master with guns and new fangled tech, plus allowing for four player split-screen for people who had that many friends.
Although, obviously, any time we think that a game should be remade we should think of the numerous horrible remakes of Sensible Soccer there has been - sometimes technology and attempting to 'stay loyal' to the original just complicates things too far.
And Psychonauts, ignored by many, but loved by games reviewers.
I think there's a few games with sequels already; but that the series could do with a reboot of sorts - I'm thinking along the lines of Syndicate, Gauntlet, Thief, Shadow of the Beast...