- Estimated achievement difficulty: 5/10
- Offline: 60 
- Online: 0 
- Approximate time: 30 hours
- Minimum number of play-throughs needed: 1 [Case Select]
- Missable achievements: 0 [Case Select]
- Does difficulty affect Achievements?: No
- Unobtainable/glitched achievements?: No
Amid the post-war boom of Hollywood's Golden Age, Cole Phelps is an LAPD detective thrown headfirst into a city drowning in its own success. Corruption is rampant, the drug trade is exploding, and murder rates are at an all-time high.
In his fight to climb the ranks and do what’s right, Phelps must unravel the truth behind a string of arson attacks, racketeering conspiracies and brutal murders, battling the L.A. underworld and even members of his own department to uncover a secret that could shake the city to its rotten core.
To complete the game with the maximum completion percentage you're going to have to 5 star all cases from the Traffic part of the game onwards. This means you'll need to make sure you find the majority of the clues, branch all the interrogation questions correctly and have minimal vehicle/city damage and civilian injuries. In some cases you'll also need to make sure you pick the right suspect to charge. Sometimes it may seem that both are guilty, but charging the wrong one will only net you 4 stars, whereas charging the other will get you the 5 star rating you need. Failing these will hinder your final case rating. You can miss a few clues, get a question or two wrong and cause a little bit of damage (not all of these in one case) and still obtain a 5 star rating, so don't fret. Have your partner drive everywhere and search every little spot of a crime scene and/or suspect's house, so you have all the clues. You'll also be wanting to pick up the 13 newspapers from certain cases. If you do miss some, you can go back into the case and find them.
There are a fair few miscellaneous achievements to gain and most of them are case-based. You'll be gaining most of these during your story run-through, so look out for them. If by any chance you miss some, don't worry. The game has a replay case and free roam feature, so you can go back into the game at any certain point to obtain them! Anything along the line of street crimes, I'd leave until last. A lot of these involve car chases and this is only going to rack up the chance of you causing city damage etc. Doing so will then bring your 5 star rating down for your current case.
L.A. Noire has multiple collectables you'll need to gather. Some you'll come across as you play through the cases but others are best to leave until the end - like the cars and film reels. When playing through the game, make sure you look out for the newspapers. Missing some of these may make you have to play through a case again right to the end just to pick it up. The same goes with the cars. As you play, look at the cars you drive by. If you notice one you haven't driven yet, block it off and take control of it. Doing this will help you in the long run.
DLC: A Slip of the Tongue:
This DLC Traffic Desk Case can be started from the Main Menu -> Case Selection. There is one story-related achievement that cannot be missed. It will be obtained once you have completed the entire case. In the beginning of the case, chase Cliff Harrison in your vehicle and stop his car by any means before before your backup forms a road block. This will unlock Nowhere In A Hurry. Later in the case, when you interrogate Jean Archer, you must choose all the correct responses for Femme Imbécile. During the Industrial Street raid, you can get Chop Shop by running to the building's back door and shooting the engine that is suspended from the rafters right away in order to kill an enemy. After the shootout, and after you interrogate Bigelow, check the desk behind him to inspect the Marquee-printed pink slips to unlock Racing for Pinks.
DLC: The Naked City:
This DLC Vice Case can be started from the Main Menu -> Case Selection. There is one story-related achievement that cannot be missed. It will be obtained once you have completed the entire case. In the beginning of the case, you can obtain Good-Looking Corpse when you're at the murder scene searching for clues. Just make sure to check for all four of the narcotics in the apartment. About halfway through the case you will have to tail a suspect named Henry Arnett without being noticed for Fakeloo. The first half of the tail will be in a car, while the second half is on foot. If you mess up just quit out and reload your checkpoint/last save. Toward the end of the case you will need to escort Mrs. Evestrom's daughter to Arnett's without damaging your vehicle. This will net you Chauffeur Service. Lastly, at the very end of this case, you will need to shoot out all the letters in the "Broadway" sign at the top of the hotel-case sequence. Make sure you do this BEFORE shooting the suspect to obtain Give My Regards.
DLC: Nicholson Electroplating:
This DLC Arson Case can be started from the Main Menu -> Case Selection. There is one story-related achievement that cannot be missed. It will be obtained once you have completed the entire case. In the beginning of the case, you will be asked to search for clues at the Explosion-Site. Look around for the officer who asks you to inspect the metal debris near him. Once you have inspected the clue and solved the puzzle, you will get The Nose Knows. Later on, you will need to investigate Tomoko Okamoto's apartment and search for clues. In his apartment, make sure you inspect all four clues to unlock Skeletons In The Icebox. Towards the end of this case, you will need to investigate the a house, which soon gets torched by a Molotov cocktail. Escape from the burning house and pursue Vernon Mapes to Hughes' Aircraft in order to get Out Of The Frying Pan. Once you are at Hughes' Aircraft, a gunfight will begin. In order to obtain Bulletproof Windshield, you will need to kill two different drivers before they pull up and get out of their vehicles. There are four different opportunities to do this. If you fail, let the enemies kill you and try again.
DLC: Reefer Madness:
This DLC Vice Case can be started from the Main Menu -> Case Selection. There is one story-related achievement that cannot be missed. It will be obtained once you have completed the entire case. Throughout this case, you will find some US Morgan silver dollars. The first can be found on the body of Cruz, the second will be given to you at the Market, and the last two can be found after Parnell's Soup shootout. Once you have all four, you must solve a letter puzzle on them. Organize the coins so the letters appear as: MAS-ANG-KAY-MET-ALS. Once you cmplete this puzzle, you will unlock Spare A Dime. In the beginning of the case, go ahead and meet Freddie Calhoun. You will then have to drive to Juan Garcia Cruz's house. After some cut-scenes and a shootout at Cruz's house, you can obtain Forcible Rear Entry by running alongside the wooden fence near your cover and entering Cruz's house from the back door. Soup In The Pot and High Flyer can be obtained right after the shootout. First, go outside into the backyard. Head inside the wooden shed and inspect the shelves to find a lever-soup-can that opens up a secret room. In this room, use the can opener on the wall to open both soup cans for your achievement. After this, head back into the house and into Cruz's bedroom. Inspect the newspaper on the ground with an advertisement for 20th Century Market. Head straight to the Market for your achievement.
Overall L.A. Noire isn't a tough 1k by any standards, it's just a little time consuming if you miss getting a 5 star rating on some cases and then there's the cars/film reel collectables to take into account.
[x360a would like to thank BiggD for the DLC additions]