Battle for Icecrown is another "old school" classic. It was notably selected by Blizzard as one of their spotlight maps, and is the only AoS I'm aware of to date which explored implementing a dynamic terrain.
Rather than the usual river and pair of opposing towers, the middle lane in Icecrown sports six large platforms which periodically raise and lower, changing the layout of the lane. Despite sounding complicated, it's really just switching between two configurations every minute, but this has some interesting consequences for gameplay.
The (Shifting) Lanes
Essentially, the troops on the middle lane alternate between fighting at the top river crossing and the bottom river crossing:
While they're fighting on one crossing, the other is walled off and inaccessible. As well as forcing heroes to position themselves carefully lest they be walled out or trapped, this system also means that if there are survivors from a wave of troops, they are allowed to beat on the enemy tower uncontested (because the next wave is arriving at the other crossing - which is walled off!).
To accommodate for the confusion, there's a 50% experience bonus for being on the middle lane. Also, the Staff of Teleportation item is dirt cheap and an easy solution to being trapped or walled out - with a 5 second channel you can teleport to any friendly unit.
Other than the middle lane, the terrain follows a very standard 3-lane formula.
Items and Shops
Items are fairly standard derivatives of Warcraft's default ones, though there are a few notable shops. The (only) shop in each team's base offers very limited selection, but another shop not far outside offers slightly more variety (such as boots and regen items).
A unique Kobold shop between the bottom and mid lanes sells a number of strong items which don't become available until 10+ minutes into the game.
There are a pair of hidden shops which only appear when the player stands in a certain place for several seconds (thankfully the specifics are mentioned in the tips for new players). Their presentation is quite elaborate!
Finally, there is a shop atop a seemingly inaccessible mountain which is dedicated to selling gems - items which have a chance to cast a spell on the target you're attacking with each attack (30% against non-heroes, 10% against heroes). The spells include sleeps, slows, damage, banishes, snares, applying a miss-chance, or even stealing summoned units! However, they don't stack with each-other at all.
One feature that seems a little crazy is that heroes can randomly drop items on death, which probably wouldn't fly in a modern moba.
Thankfully there are a number of less risky ways to spend your hard earned gold. One option is consumables, because they can be used before you die. Among these is a staff of dispel which claims to dispel mines and wards (!) as well as any other summoned units and buffs in the target area. Sadly, there aren't any purchasable wards in the map to make this useful for a warding meta.
Another option for non-risky spending is to invest in Troop Upgrades, which can either improve the attack damage/armour of your troops, or upgrade your team's melee troops to a heavy melee troop.
If you can catch the Zeppelin flying around the map and have 5000 gold to spare, you can buy a new unit production building which produces goblin sappers: suicidal units which explode into the first enemy they come across. They're particularly effective against buildings, and once the building has been bought the zeppelin vanishes from the map.
It's also possible to drop 1000 gold on a new tower, which your hero can place anywhere they can reach. This is potentially useful for pushing, or maybe having somewhere in enemy territory to teleport to, but towers aren't particularly durable so they're best for reinforcing your existing defences.
There are over 60 heroes in the map, but around 15 of these are random-only, and several others are "secret" heroes. This appears to be inspired by the secret in Eul's DotA, where approaching an NPC on the map with the right combination of items in-hand would allow players to play as that NPC. Icecrown has several such NPCs to choose from.
The heroes themselves vary between standard ladder heroes from Warcraft to some interesting concepts which couldn't be fleshed out fully with the editing knowledge available in 2004.
Once such hero is the Banshee, who is permanently ethereal (can only be damaged by spells), so she can roam freely past enemy towers and units. Her ultimate allows her to possess a non-hero unit, giving her abilities and stats to their body, with a primary attribute depending on the unit possessed. She can become a ghost again and switch bodies with no cooldown, but the mana cost is steep.
Battle for Icecrown is a solid AoS for its era, but like most it hasn't aged well. Too many mechanics don't contribute to lasting gameplay, and they choke out the better ones.
I would be excited to see how the terrain dynamics Icecrown pioneered might be used in a more modern AoS: there is plenty of potential for creative application and interesting results.