The advantage of D&D, and roleplaying games in general, over other interactive media like video games is that you have human-level intelligences deciding what happens next instead of a more-or-less dumb AI system operating in a pre-programmed game engine with pre-made art assets. There are no "invisible walls" that you can't go through, or actions that are impossible just because there isn't programming for it. If you were playing an RPG of Dragon Age*, you could flirt with any NPC, not just the pre-programmed ones; travel to any location you can get to, not just the ones that they put in the game; try any action, not just the ones there are buttons for.
When you have a human GM† running the game reality instead of a computer, you've got all that flexibility – the only limitation is how quickly they can come up with creative answers to unexpected turns of events. In fact, the very defining experience of a DM is that moment where, despite all your preparation, the players go and do something totally unexpected. It happens to all of us, and the skill of GMing is often summed up by how much skill (and practice — it's totally something that gets better with time and practice) you have in responding to these unexpected choices of the players'.
An important feature of roleplaying is ownership. Your group's play experience is entirely your own to enjoy, and your own to make enjoyable. You get out what you put in. What adventures you play, whether they are published or not, will ultimately be unique in the end experience to your group. There's no way to reproduce perfectly what the designers intended, because they never did intend any such thing: every game and every adventure is designed with the awareness that it will never be played the same twice. So take advantage of that flexibility to make your play experience as enjoyable as you can!
* There is, in fact, a Dragon Age: Dark Fantasy Roleplaying game.
† "GM" or "game master" is the generic term for the person's role. Some games have a more specific term, like D&D's "DM" or "dungeon master".