Many of the mechanical RPG elements that are tropes/clichés today, were also created or popularized by D&D. The Class and Level System, Hit Points (arguably present in the tabletop wargames that preceded D&D, but named and popularized by D&D nonetheless), Character Alignment, the "+ 1 magic sword," and so on.
D&D is very likely the single most influential game ever, in terms of what it started and popularized, stretching even outside of the RPG genre. Its influence on video games was enormous and not to be underestimated.
Conversely, more tropes in High Fantasynovels work as codified in D&D, instead of as seen in Tolkien. You're more likely to see Magic A Is Magic A than Tolkien's deliberately mythical and mystical style, for instance.
Magic: The Gathering single-handedly invented the Collectible Card Game. Games like Yu-Gi-Oh and Chaotic owe their very existence to a man named Garfield. Yet, because of those games, Magic is sometimes dismissed as a children's card game. This despite the fact that many big-time poker players began honing their skills on Magic, and a small but significant group of people make their livings out of tournament winnings and appearance fees.
Just as in Magic: The Gathering, Yu-Gi-Oh! features this as well - many cards that were hot stuff or "I Win" buttons back in the day are now in the modern day practically useless - if not outright banned from tournaments. Yet the modern metagames of both require many strategies that were created amongst the early years of both games.
As an extension: the earliest deck with a name in Magic is simply The Deck. The Deck was built with the philosophy of keeping as many cards in your hand as possible, to be able to readily respond to your opponent. Back then, the idea was revolutionary, and The Deck swept tournaments. These days, the philosophy of the deck is call Card Advantage, and it's one of the first things you teach players wanting to get better.
For Warhammer 40,000, their eponymous Space Marines are considered something of an unfunny by some of the fanbase. The Space Marines and their incarnations are arguably the most popular faction, and thus a lot of ire is directed at them from players of other armies. Reasons for Space Marine popularity include: the easy difficulty curve and relative forgiveness of the army book, the regularity with which the main codex is updated, being one of the 'more acceptable' armies for children to play, and in general receiving the bulk of support from Games Workshop. Thus it is that Space Marines can sometimes be considered an 'unfunny', 'scrub', or 'kiddie' army.
Don't forget that the small army size and inclusion in every starter set ever also make them among the cheapest.
The large metallic surfaces of the power armor that the space marines wear is also a lot easier to paint than the flesh and bone of many of the other armies (imperial guard, orcs, tyranid, dark eldar).
Admittedly the reason the Marines are comparatively kid-friendly is that no less than four of the other armies consider mass murder (Orks), arson (Sororitas) and rape while torturing people (Dark Eldar) or all three at the same time (Chaos) a fun way to pass the time.
This also caused some of the lore seem weird by comparison. Most notably the Bolter; it's essentially a rapid-firing grenade launcher that can take off entire armored limbs in one shot. Most people decry it as having nowhere near the amount of power as depicted by the lore. However, originally a 5+ armor save (which a Bolter easily ignores) was considered heavy armor back in the inception of 40k, which was originally based on Warhammer Fantasy, and the baseline for toughness, strength, weapon skill and so on was 3, meaning the Bolter's Strength of 4 was well ahead of the curve. But due to Space Marines being far more popular than any of the other races (especially the Imperial Guard, who were supposed to be a badass army) they instead became the baseline, to which everything else was measured against. Most people nowadays forget that Space Marine Power Armor is supposed to be equivallent to tank armor, which is why they take so little casualties from small-arms fire.
The Settlers of Catan - which has only been around since 1995 introduced many concepts to a wide audience for the first time that are yawnworthy today. Among them is fully embracing a layout that changes for and with every game and a simplified way of teaching the rules to novice players (the German version of the rulebook even won a prize for clarity). None of that is considered particularly new today and neither is the tendency to cash into the hype of a boardgame with expansion packs and second or third editions and the likes.