Heroes, in a nutshell, is a game in which two teams are trying to destroy the Core of the opposing team. The Core is similar to the Ancient in DotA or the Nexus in League. Each team has a base with Forts, Towers, Gates, Healing Wells, and Walls to help them defend their core.
At regular intervals waves of NPC Minions spawn in each base and march down pre-defined lanes to attack the enemy. It is the job of the players to help attack down these lanes and destroy the enemy team's base and ultimately their Core. To help with this, each of the maps has a special map objective that gives a big bonus of some sort to the team that completes the objective. Generally each objective will be completed 3-5 times per match before the core is destroyed.
Just like the waves of NPC Minions who spawn and march towards each other in battle, so too do the player characters respawn when they die and continue to fight. The amount of time it takes to respawn is directly related to how long the game has been running. In a new game that is only minutes old, a player will respawn almost immediately. In games over 15 minutes in length the spawn timers will reach a full 60 seconds.
Core: The first team to destroy their opponent's Core wins the map. The Core has a recharging shield which is worth about 15% of the total health of the Core. This shield regenerates very quickly when the Core is out of combat for 8 seconds. The Core also shoots a lightning blast at a target that will also damage enemies near that target. It follows the same targeting rules as Forts and Towers (see below), but is immune to many effect that shut down structures.
Tower: The first line of defense in each base. Towers have limited ammo which regenerates over time. Towers prioritize minions and summoned units and will ignore player characters as long as there is a minion or summoned unit within range. Unlike other MOBAs, the Towers in Heroes will not target a player character if that character attacks an enemy hero while within range.
Forts: Each lane has one Fort, which is located behind a wall and two towers. These Forts have a lot of HP and attack with ammo just like Towers do, but they also slow enemy movement and attack speed which makes them a decent place to defend from. Destroying a Fort yields a considerable XP payout, making them primary targets in the early game.
Keeps: After a Fort, the last line of a lane's defense before the Core are Keeps. These function similarly to Forts, and will also pay out big XP if destroyed. If a keep is destroyed, the opposing lane will start spawning long-range, high-damage catapults alongside the usual minions. Therefore, it's very important protect your keeps while destroying your opponents'.
Healing Wells: If you have played Warcraft 3 then you are probably familiar with the Healing Wells, as they operate similarly to the Moon Wells of the Night Elves. They are on a timer, and restore Health and Mana when you click them. The Health and Mana provided by these Wells is not instant, as the restoration happens over time.
Spawn Point: Each team spawns behind their Core in the safety of their base. There is a magical shield barrier that prevents the enemy team from entering the spawn location, and this shield stops all spells and attacks. Spawn Points also have instant-mounting while you are inside, and you regenerate Health and Mana at a very fast rate while standing in the spawn.
Minions spawn down the lane like merry lemmings just waiting to die to a tower or hero. They are...
1. Soldiers: Dudes with swords, they lead the minion waves. Tend to have higher-than-average HP and a weak melee attack.
2. Archers: Dudes with, get this, bows. They're in the back of the wave, boasting lower HP but a decent ranged attack.
3. Mages: Wizards that coast in the middle of the pack. They deal ranged damage, but the more important thing is that they drop a green orb on death that will give you and nearby teammates a little bit of HP and mana back. There's only one per minion wave, so try to get that orb!
4. Catapults: Beefy siege units that assault bases with a long-range attack. They only spawn when the enemy's final fort in that lane has fallen, giving you incentive to keep that damn fort alive. They can easily outrange towers/forts/cores, meaning they will slowly whittle down a base unless stopped.
Each map also contains a scattering of Mercenary Camps in the "jungle" area between the lanes. These Merc Camps are neutral NPCs that can be defeated by players and hired to fight for the team that captures them. To capture a Mercenary Camp, the players must defeat them in combat (or bribe them) and then stand within a capture circle for a few seconds to gain control of the camp. It is possible for the enemy team to steal the camps if they push you out of the circle or kill you before you can claim it.
1. Siege Camps: These camps contain two giant siege monsters which hurl large rocks at their enemies. They have long range and can out-range towers and forts, which make them very advantageous for lane pushing. These are the easiest camps to defeat and can be solo'd by most heroes by level 10.
2. Bruiser Camps: Formerly known as the "Knight Camps," these are squads of 4 soldiers (3 melee and 1 spellcaster) who possess a lot of HP and decent damage damage. These camps are more difficult to take and typically require 1-2 people to capture.
3. Boss Camps: These camps generally require 3+ heroes to kill, depending on team levels and what heroes are present. These are high HP / high Damage monsters that can do devastating amounts of damage in a lane. They ignore minions and other mercenaries and will only target enemy structures. They cast a Pound skill that can be avoided by moving out of the telegraphed smash circle. They also cast a targeted root spell on occasion against enemy heroes, telegraphed by a smaller circle.
4. Map-Specific Creeps: From pirates on Blackheart Bay to the plant monsters in the Garden of Terror, these mercs will NOT join your side, but instead drop objective-relevant items that help you win the game like skulls, coins, and so on. Difficulty and rewards vary by map.
So what else? There is no item shop. No in-game gold. No items to be bought. No shoes or rods of whatever. "Blasphemy!" you might say, but Heroes is feeling pretty heretical. Instead of items, you get talents roughly every 3-4 levels. These are anywhere from 2-5 choices that change how your character functions. It might be "killing minions gives you more damage" or "your auto-attacks now slow enemies." At level 10 you unlock your Heroic Ability (aka your ult), and even that has choices! Every character has two heroic abilities, so pick the one most suited for the current game.
If you have played other MOBAs and are accustomed to buying boots, this game doesn't have them. Instead it has Mounts (default Z key). Attacking or taking damage dismounts you, and re-mounting does have a brief cooldown. Not all characters can mount up, but instead have mobility skills that in most cases let them get to an area REALLY FAST but has a much longer cooldown.