"The infantry have for their defence a breast plate of iron, and for offense a lance nine armlengths long, which they call a pike, and a sword at their side, rather round in the point than sharp. This is the ordinary armament of the infantry today, for few have their arms and shins (protected by) armour..."
— Niccoló Machiavelli, The Art of War, Bk II
Clasped in armour and trained to perfection, Hoplites are the beating heart of Axial Age Greek and Etruscan armies. They are costly to maintain and slow, yet do what they do best - holding the line and grinding down less well-armoured armies to a fault.
Hoplites replace all spear units — the so-called "Long Spearmen" squads included, so any Long Spearmen you may have recruited will doubtlessly be replaced. However, their strength isn't in hosing melee units or deterring cavalry, but in their tight cohesion, their resistance, and their mobility and rate of attack. The Hoplite is thus a very powerful unit when used in the ancient way — mass them at the site of battle, and then send them plunging into the foe. Of course, their lack of armour means that they are easy prey for arrows, but Hoplites were never meant to function in isolation. An army of Hoplites, protected by light missile infantry and amassed horsemen will always be able to hold their own.
Note, however, that as units go, Hoplites are still poor choices when used to assault buildings. True it may be that their killing power makes them the queen of battle but for urban warfare, you will have little choice but to fall back on either Militia or Swordsmen to do your bidding. An army of Hoplites escorted with siege weapons and ranged units is thus a wise choice. If you were on the receiving end, however, consider fast ranged units. Medium and heavy chariot units armed with composite bows, horse archers or Elephants are all ideal units for use against Hoplite formations......or any spear units for that matter.
The predominate Greek soldier of antiquity was the Hoplite, named after the great round shield he carried into battle. Hoplites wore helmets, leg armor, and chest armor, and carried a great long spear. They fought in dense columns with the spear points from several ranks projecting out from the formation. They thus presented a formidable block bristling with spears held above the shoulder. In battle they would close with the enemy as a pushing wall of shields, stabbing with their spears over the shields. Men behind would push those in front and stab over them. This fighting was face-to-face and terrifying, requiring high skill and discipline. Battles were usually short but deadly. Before the rise of the Hoplite, most army fighting had been more long-range archery and posturing. The Greeks made war personal and intense, and Hoplites dominated ancient battlefields for centuries.