Man, that was a lengthy game! I guess any open world game, such as L.A. Noire,  is bound to be lengthy since you have the ability to explore the world at your own leisure. This game was getting a lot of 5-star ratings, which is why I decided to play it (the star studded cast was also another major motivator).  Having played and finished the game I think that it is indeed a 5-star game! (now, where is the sequel? ;-)  )

In terms of just plain-ol' metrics, I finished the game with 24 our of 40 achievements; more than 50% ain't bad, but I would have loved to have had at least 30 of them, maybe on the second time around? ;-). There were a few achievements that I guess I could have gotten had I played my cards right from the start.  For example

• I got 12/13 newspapers (must have missed one early on), 
• I solved 30/40 street crimes (I meant to do all of them, but once I got to Arson Squad, case #3, I stopped seeing them.  I guess more exploration of the map)
• I got 46/96 cars (this was the least enjoyable since I got in and out of other people's cars.  I know that as a cop I could commandeer a car, but it just felt weird to do so.)
• I leveled to level 18.5.  I think I could have made it to 20 if I did a few things differently.
• I don't even remember how many monuments I discovered...