The Middle Ages is a big subject that covers a vast geography and time, so nothing can be said universally about it, but certainly in the periods I'm familiar with, which would be c.1100 to c.1600 Western Europe, opposed landings were largely unheard of.

We should take a moment to consider what is meant by an opposed landing - if we mean that any opposition was offered to the invading force, no matter how token, then I suppose opposed landings would have been reasonably common. While some medieval ships were capable of beach landings, most famously the longships popularly but not exclusively used by vikings, many were not and had to find a proper port to land their ships. Now, most ports in enemy territory weren't going to let you drop off your entire army without at least a little opposition, but also the garrison of a small port city was not really able to withstand the full might of an invading army so it's not like they were going to fight to the death. Standard practice in a siege where you were vastly outnumbered would be to resist initially, then sue for peace - if you held out to the bitter end the attacker was not obliged to spare your lives by the social norms of the time, and often wouldn't.

From what I can tell from a cursory online search Dan Jones is planning to fictionalise the Crécy campaign of 1346, which is a particularly odd choice for this kind of thing since Edward III's army famously faced remarkably little opposition to their landing in Normandy. If we're feeling enormously pedantic, Edward III's fleet landed at St-Vaast La Hougue, which is a little east of Cherbourg and were any ships to land on the beaches nearby that would be Utah Beach, not Omaha (although any WWII specialist can correct me, the beaches of D-Day are not my area). Realistically, most ships would have disembarked in the port of the small city. The level of opposition posed to Edward by the people of St-Vaast was so minimal it barely gets reported in contemporary chronicles, it is assumed that Edward would be able to take the city with minimal effort.

The obvious question is why would Edward III be so lightly opposed? There's a few answers. The first is that it was difficult to establish where a medieval fleet was actually going. There's no air reconnaissance or live updates on the enemy's preparation, the French would have been entirely reliant upon spies who would be restricted to similar means of travel as that of Edward's own army. Naval travel at the time was highly unpredictable, Richard I's crusading fleet famously got shipwrecked on Cyprus while sailing for Acre. Even more common than shipwrecks was being blown off course, or simply being able to unable leave port on time because the wind wasn't favourable. There is a line of argument that Edward actually intended to invade via Gascony - largely friendly territory that had been ruled by English kings since Edward I, albeit a bit intermittently as French kings were prone to seizing it whenever the two monarchs were in conflict. This argument goes that he was blown off course up towards the Isle of Wight, and instead of landing and resupply chose to travel instead to Normandy and disembark there - a much shorter journey from his new location.

Andrew Ayton has pushed back against this theory, suggesting that Edward implied that he was going to Gascony to confuse the French king and always intended to travel to Normandy - he just kept that fact a secret from all but his closest advisors. I don't have time to re-tread his whole argument, but I think it's reasonably convincing. In any case, France has a large coast and the French king couldn't be sure where exactly the English would show up. Similarly he couldn't be sure of when, and maintaining garrisons was expensive. There was no standing army so any attempt to oppose the landing of an invading force would mean assembling and paying an army for just that purpose - but then how long do you keep them in the field? You could pay them to be nearby for the summer, the main season you might expect an invasion, but then late season invasions happened - William the Conqueror landed in England in late September. There's even a story that 500 Genoese crossbowmen had left St-Vaast shortly before Edward arrived due to not being paid on time (a common problem for mercenaries, medieval monarchs were not timely in settling their debts).

Another thing that would stop an opposed landing would be to simply land in friendly territory. After Crécy Edward III took the port city of Calais, which the English would hold until the time of the Tudors. Many invading forces landed in the friendly region of Calais rather than attempting to disembark in enemy territory. Another option if you didn't hold territory in your enemy's lands, would be to land in an allies territory. Medieval wars were often fought on the back of an alliance, so for example the English king might agree to support a noble against the French monarch - then he could land in that noble's lands unopposed. At the very start of the Hundred Years War, Edward had unsuccessfully invaded France via the Low Countries (modern day Belgium) - a region whose loyalties were pretty regularly swinging between France and England at the time.

There are some examples of events that arguably represent a type of opposed landing, although nothing quite like D-Day or any modern amphibious landing campaign. The most famous is probably Richard I relieving the city of Jaffa. The short version is that Saladin besieged the port city of Jaffa while Richard and much of his army was up north in Acre in 1192. Richard gathered together a fleet filled mostly with Italian mercenaries, and after several delays due to unhelpful weather, sailed south to relieve the city. Richard reportedly leapt from his boat into the surf of the beach and stormed the town, shooting his crossbow as he went. Saladin's forces were driven from the city, and the two fought a pitched battle outside the city a few days after, which Richard also won. This is about as close to D-Day as you're going to get, but Richard was landing near a friendly citadel that was under siege and driving off an attacking army that was out of formation and ill-prepared for a pitched battle. Saladin and his soldiers presumably preferred their odds in a more orderly battle later rather than in the chaos in the city when Richard first arrived (an army once dispersed was a tricky thing to reassemble).

Another case of opposed landings could be seen in river raids, although again the situation doesn't quite line up. The vikings were famous for raiding up rivers in France, but the practice continued into the Later Middle Ages - especially in the Baltic Sea region where there were fewer cities to block access up the rivers. During these raids an invading force might travel up the river until they met opposition (or were stopped by a feature such as a defended bridge or city that spanned the river), then they would plunder and possibly fight any smaller sized army they came across. The frequency with which these ships were opposed when landing was definitely much higher than, say, the fleets of Edward III during the Hundred Years War, but at the same time their opposition was kind of the point. If they were unopposed these fleets generally wouldn't bother landing, and once they reached somewhere worth sacking or that impeded their progress, they would stop and fight (not to say that raiders didn't sometimes stop and march overland toward their target, they certainly did).

In essence, the idea of an invading fleet facing some opposition would not be unheard of, but in practice it would have been minimal and only actually succeeded in impairing the invasion on a small number of occasions. There are a number of factors for this, but the limitations of medieval intelligence networks and the inherent unreliability of medieval naval travel made any concentrated effort to locate and oppose a military landing largely impossible. Unless you happened to have your army a the right spot at the right time, you were far better off fighting a battle near the landing site than actually trying to stop them from landing. Besides, even if you did scare them off, what's to stop them from sailing down shore for a day and landing there?

For Crécy the two best books right now are Andrew Ayton and Philip Preston's The Battle of Crécy, 1346 and Michael Livingstone and Kelly DeVries' The Battle of Crécy: A Casebook.

For more general warfare, I'd recommend John France's Western Warfare in the Age of the Crusades and Michael Prestwich's Armies and Warfare in the Middle Ages.