Destiny is an online-only FPS with RPG and MMO elements. You play as a guardian, trying to save the human race from aliens.
Pro Improving your character is addicting
One of the main aspects online titles like Destiny 2 is character progression, which is done through leveling and collecting new equipment. Your character gets stronger and when you revisit missions/bosses that gave you trouble before, you can beat them with ease, which feels incredibly satisfying. This will push you to play just a bit more, collect a few more guns and armor pieces, defeat a couple more bosses, and before you know it, many hours will have passed.
Pro Massive environments that feel alive
The open-world environments in games usually have a lot of empty space, so you spend most of the time traveling without doing much else. Destiny 2 has large areas filled with enemies, world events, and activity in general, eliminating most of the downtime. Because of this it feels like you're actually visiting a planet inhabited/occupied by aliens, which considerably adds to the immersion.
Pro Solid controls that don't detract from gameplay
Your character's movement, aiming your gun, and even driving your hoverbike feels really fluid and responsive. As a result, you can make very precise movements, jumps, and shots in any situation, allowing you to land a headshot with your sniper rifle from far away while strafing with ease.
Pro Excellent co-op multiplayer
Even though Destiny 2 doesn't have strict class archetypes like most MMOs, each class/subclass has its role in a group setup. So whether you're capturing control points in a PVP match or fighting a tough boss in a raid, you still need to cover for each other's weaknesses. This can be providing support to surrounded teammates, taking the attention of groups of aliens or just picking off troublesome enemies from afar. Because of this you learn to rely on each other and working together feels rewarding.
Pro Really fun gameplay
Destiny 2 is all about killing aliens and destroying massive robots. To do this you have a wide variety of weapons and abilities available to you. This includes hand cannons, shotguns, assault rifles, chain lightning grenades, and many more. Each weapon and ability feels great to use, making destruction and mayhem that much more enjoyable. It's a well-rounded and enjoyable experience, which will keep you interested for dozens of hours.
Con Inconvenient customization
While most online games usually give you permanent color packs for customization, the shaders in Destiny 2 are divided into single colors that can only be used once. You can't preview your new color scheme either, so if you end up with something you dislike, you're stuck with it because you can't change it back. This also means you shouldn't use shaders on leveling gear since you're gonna replace it anyway. As a result most players don't bother with creating unique appearances and everyone looks nearly identical, which is bad for the social aspect of Destiny 2. The sad part is that even though the shaders can drop randomly in the game world, they can also be bought from the in-game store. This makes it feel like customization has been turned into a cash grab by inconveniencing players.
Con Guns and armor do not feel unique like in the prequel
In Destiny 1, the guns and armor felt more unique when compared to Destiny 2. In Destiny 1, a gun or armor could drop that had one set of perks or stats boosts, and then it could drop again with a different set of perks and boosts. Weapons and armor from the raids also gave unique looks as well as perks that helped for that raid. In Destiny 2 those raid perks are gone, making the gear feel no different than what could get from anywhere else. The lack of variation in the guns and armor just make it hard to care about what you get and kills the urge to try to find the best gun and armor for your character.
Con Content that was available at the start of the game ended up locked behind DLC
When the expansion Curse of Osiris was released, Bungie ended up preventing players without the expansion from being able to access the prestige versions of the first raid and nightfall strikes, as well as the PvP Iron Banner and Trials of the Nine. For the people who like to hunt achievements/trophies, this move effectively blocked them from earning them. Bungie has since patched things so players are not locked out of the prestige mode of the first raid, as well as nightfall strikes and Trials of the Nine when not using Curse of Osiris maps, making the achievements earnable again. Still, it was an extremely poor decision to lock player out of content they paid for and leaves the question as to will Bungie make another mistake with the next expansion.