I feel like an extremely linear game is utter shit because it greatly aids replayability if you have a slew of ways to tackle a given objective, other than using your shotgun or your assault rifle. So I generally enjoy games that offer sandboxes, but not necessarily just one big sandbox. If the game has your progress along a path of small, compartmentalized sandboxes, where you have an area with your objective located inside and nothing restricting how you move about (for example, Crysis 2), then that's good enough for me.