Depending on what period of time you are talking about, the tactics were indeed obsolete. This may not have been true for the Napoleonic Wars, but it was certainly true in the US Civil War. The original 'musket lines' were essentially designed for concentration of firepower due to a lack of accuracy. Before rifling, you couldn't really aim and hit anything that wasn't directly in front of your face. Large lines allowed the attackers to throw a wall of bullets forward, thus guaranteeing that something would be hit.

The invention of rifling changed this though. By the US Civil War, the guns that both sides used were relatively accurate and individual targets could be accurately hit from a reasonable distance. The fact that they kept lining up and volleying away at each other was simply a lack of tactical evolution. At that point in time, the technology had outpaced the school of military thought. The exact same mistake was made during the first few years of WWI.