I rather like games that offer some variety. Sure, when you've gained a fair mastery of the game, you can get by with the bare basics - but when you're still getting used to it, it's nice to have a bigger range to play with. MGS3, as already mentioned, is a good example. You can do it with just the tranq pistol, but the other weapons are much more appropriate for some of the fights. For instance, when fighting The Pain I always use the shotgun to get past his "I'm covered with bees!" armour, and the assault rifles are handy during the motorbike chase near the end. Then there's the sniping duel with The End, which gets all the more tense when it's sniper-against-sniper.

The same's largely true for nearly any combat-oriented game, from RPGs to third-person shooters.