i don't think it makes much sense to treat orange box as a single game, but on reflection, portal is my goty. mario galaxy is brilliantly designed, and i played the fuck out of it for a good week -- but it kind of diminishes in memory's perspective. portal is also brilliantly designed, for the one sitting it lasts -- but GLaDOS has kept it going in my head. she works as a kind of unreliable narrator, and her dark humor and bizarre personality shifts make her the best character in gaming. ever, probably. she also has a lovely singing voice.
do character and writing and music really matter in games? yes, apparently. this is also why i don't think your immediate impressions are necessarily best. sometimes your vision of a game is addled by its proximity -- you need a bit of distance to make out its stature