Although it may drag at times, LA Noire is one of the most unique games with some of the best storytelling in years.
The biggest thing about the game is probably what you've seen on the commercial, which is the level of detail in the facial features during conversations. What they did for this was stick the actor in an all-white room with 25+ cameras pointing at them from different angles so no detail is missed, and this is why the game takes up three discs on the 360. In every other game, no matter how good the graphics, you don't see anything even close to this. In most games, graphics are just something to look at and don't really add anything to the actual gameplay or story, but in LA Noire, it's probably the single most important feature since you really need to be able to read the suspects, victims, and witnesses. If LA Noire didn't have this feature, than it would kind of be like trying to figure out if someone's lying by reading something online. Pretty much impossible, and not at all fun.
So most of the missions start with you getting a case, going to the scene to find clues and question people, driving to other places, and eventually charge someone with committing the crime. Trust me, it's WAY easier said than done. When you question someone (there's a list of questions already written down for you to ask), the person will answer you and it's up to you if you think they are telling the truth, if you want to doubt them, or if you want to call them out on a lie. The difference between doubting and calling someone a liar is that you doubt someone if you THINK they're lying but don't have any hard evidence to back it up, and call someone out if you have hard evidence. Starts out pretty straightforward, but gets much harder. By selecting the correct response, you'll get more information, making it much easier to get the right person.
The story is great, although the ending is hit or miss (I thought it was great), although the middle of the game does seem to drag a little bit since you're doing the same things for a while, but the last third of the game is awesome and always keeps you guessing. After finishing each case/mission, you can then play them again anytime you want in the main menu. There's also the typical collect all the XXX side missions, in this case you have to collect all the cars, famous historic sites, hidden movie reels, and newspapers, and I'll tell you that they are WAY less annoying than the GTA collect-them-all quests. Great game, great story and storytelling, drags a bit at times, and is incredibly unique. Unless you're expecting a game that you can just run around and shoot everyone or a game that MUST have online multiplayer, I think you'll like this game.