Great Game Mechanics

Some games are defined by a few core game mechanics. Sometimes, these mechanics are also what makes these games great. For example, you have Realm of the Mad God, with it's perma death mechanic. Each time you die, your character is deleted. All the items that were equipped, any items that were used by that character and any levels are deleted forever. The only things you could keep, were things you stored away in your vault ahead of time. This kind of harsh game mechanic is one you rarely ever see and really makes that game stand out. Each death is a learning experience and with each death the better you'll become at avoiding it.

Some games like Hollow Knight don't show any indication of enemy hp values. In a game as hard as Hollow Knight, where you will definitely die against the bosses, not knowing how much hp the boss has left will make you feel tense throughout the whole fight. You never know if the boss will have a second, third or even fourth phase. Heck, the boss might even still have been on 95% hp when you died. There's just no way to know how close you were to beating the boss until you finally beat it. With each try, you'll get further. You'll start to learn the mechanics and patterns and eventually, earn that victory.

Another cool mechanic Hollow Knight has, is that death causes you to lose your spirit, aka all your money. Your spirit will stay at your death location and you'll need to journey back and kill it to reabsorb it and regain your money. If you die a second time, your money will be gone for good. (the spirit also fights back) Hollow Knight has a lot of awesome mechanics, but it'd get repetitive if I only covered it, so I'm might cover them another time.

Other games like Monster Hunter also don't indicate enemy hp, however that game series in particular has visual effects that are pretty universal across all monsters. You'll be able to estimate the remaining health based on a multitude of aspects like if the monster is limping, how many parts you've broken, etc. That kind of mechanic encourages you to pay attention to the small details.

Games that use checkpoints generate artificial difficulty by making it impossible to quick save. They can also encourage you to play less because you won't be able to just play another 5 minutes.

Games like Ark just really screw you over with the amount of resources needed for anything and the abysmal amount you can gather on default settings. Carry weight limitations just makes that process a whole lot more annoying.