I also remember reading that the landings at Gallipoli caused a complete overhaul of amphibious landings and how they were fought. What specific events/factors in Gallipoli did military's learn the most from and what specific reforms did they implement to avoid repeating these mishaps?

Surprisingly, this BBC article on Gallipoli gives a good summary on lessons learned from Gallipoli that were implemented in WW2:

There can be no doubt that the lessons of the Gallipoli landings were at the forefront of many of the planners' minds. They had grasped the vital necessity for an adequate period of planning for all three services - the army, navy and air force. Experts of all kinds were required for all phases of the planning and operations. These needed to communicate properly with each other to ensure that everything was ready for use as and when required

One of the big problems in military operations - something that exists to this day - is the lack of communication between branches. Militaries are often portrayed as monolithic entities but in reality, they are nearly independent branches consisting of semi-autonomous subcommands that have to coordinate with one another.

One of the big lessons learned from WWI on the Western Front, and directly applied to WWII, was that there was to be no ambiguity in who would be the Supreme Commander in Allied Forces - they chose Ike and there would be no question who was at the top of the chain of command.

Amphibious operations, in particularly, are a very complex beast requiring simultaneous coordination between ground forces, naval forces, and air forces. The lack of coordination between forces in Gallipoli may seem silly in hindsight, but that was how militaries often worked: the Army wanted something, and the Navy wanted something else, and the two would often clash about how to do it. For instance, the Navy might not want to sail ships into close range of enemy guns or minefields and would resist taking out risky targets - however, the Army would want those targets neutralized to make their landings easier, often without consideration for the dangers to the Navy, etc. And there would be little way around it: the Admiral in charge of the fleet may have complete authority over the ships in the region, while the General in charge of the ground forces may have complete authority over ground forces, and no one could tell the other otherwise.

Note that these problems weren't entirely fixed in WW2 - in fact, for the US, it wasn't until after the Invasion of Grenada in 1983 which saw failures of communication between the branches, saw the Goldwater–Nichols Department of Defense Reorganization Act of 1986 passed which entirely reworked the organization of the DOD to include more joint unified combatant commands so that there would be less infighting, confusion, and lack of coordination between the armed forces in joint operations

The importance of accurate intelligence was now understood - not just accurate maps, but detailed information on local topography, offshore navigational details, prevailing sea currents, ground conditions, water supply, prevailing weather patterns and the exact nature and strength of enemy dispositions.

Even then, these lessons would be hard learned during WW2 in places like the Battle of Tarawa, where oceanography charts from the 19th century were used, which didn't account for the fact that boats couldn't get over some of the coral reefs and sandbars out at shore. This resulted in many Marines having to wade ashore under enemy fire - and many drowned under the weight of their gear.

The US also created the Underwater Demolition Teams (UDT), or frogmen, the forerunners of the Navy SEALs, who would swim ahead of the invasion force and scout for underwater obstacles and destroy enemy defenses.

Also very importantly, militaries around the world bolstered their oceanographical and meteorological capabilities, including today where satellites can provide accurate surveys of the ocean floor.

The flexibility of sea power would be used to transport a huge force to attack the identified point of weakness in Normandy, to maximise surprise and thereby to secure a temporary local superiority. Meanwhile sophisticated deception schemes would draw away and delay the deployment of German reserves.

One of the key lessons learned from Gallipoli was that an invasion was most vulnerable if the invasion force could not achieve local superiority quickly and was thus relegated on or close to the original landing beaches. Thus, the Allies spent considerable time and effort emphasizing surprise and local superiority in amphibious operations of WW2.

When they didn't quite do so, in places like Anzio where the invasion force was bogged down, a protracted stalemate and heavy casualties resulted, as predicted.

During the landing itself hundreds of modern landing craft would crash onto the beach simultaneously to minimise the 'defile' aspect of landing from open boats under heavy fire. New technology would be used to control the heavy guns of British battleships and heavy cruisers, to target and eliminate German strongpoints.

By the end of WW2, these increasingly sophisticated and specialized landing craft were used to maximize the number of troops that can be sent ashore at a time. Many of these ships had very shallow drafts and could land troops directly onto shore and do it quickly, to exploit weak points in defenses and to overwhelm the defenders.

In addition, the militaries of the world also improved their amphibious assault craft. No longer would open ships be preferred - amphibious tracked vehicles, like the Amphibious Assault Vehicle, would provide armored capabilities to land troops ashore as well as provide immediate armor inland past the beach. The advent of hovercraft, like the Landing Craft Air Cushion (LCAC), also meant that heavy equipment and large troops can be landed quickly on beaches of all sorts, where ships cannot reach.

Finally, after WW2, the advent of the helicopter has changed the dynamic of amphibious warfare. Now, troops could be landed far quicker than by ship anywhere at or behind enemy beach defenses. Since the 1960s, navies around the world started building the "landing platform, helicopter" type of amphibious assault ship where a large landing deck (making them appear like small aircraft carriers) capable of sustaining heavy helicopter operations would land troops directly from ship to shore, completely ignoring or bypassing disadvantageous terrain