Reviews are frequently based on a comparison of the reviewer's expectations with the actual product. I didn't have any expectations for Destiny, which is why my impression of the game is generally a positive one. I've been playing a Titan up to level 10, through all content of Earth and some content on the moon. And as I don't play so many shooters, and especially not console shooters, if anything I was positively surprised how much fun Destiny is. Apparently the game was hyped a lot before release, and many reviewers correctly pointed out that the game isn't the second coming, but as I said, it depends on what expectations you have.
That is not only a problem for reviewers, but also for players. Destiny is a hybrid between a shooter, and a MMORPG, on a console. Which means it suffers from certain limitations of shooter games, of MMORPG games, and of console games. People very much involved with one genre tend to overlook the inherent limitations of that genre, but with a hybrid game the fans of each genre discover the flaws of the other genre, and that can grate. Plus if you usually play on a PC, the console brings some extra problems, like long loading times and fiddly controls.
The world of Destiny is a curious mix of MMORPG open world zones and linear shooter levels. That isn't just visually, but the rules actually change if you leave the open world and enter a shooter level: Suddenly your respawning is limited, and death brings you back to a checkpoint, resetting all events back up to there. But because it is an online game, there is no pause function. Too bad for you if your phone or doorbell rings, or there is some other real life intrusion. On the positive side your checkpoint is saved even if you log out, so you can resume the action at that point the next day. You can even first fly back to the central hub, The Tower, identify found items, buy some new gear, and then continue in the middle of the fight where you were. You can use that to get around the silly feature that if you die because you ran out of ammo, you'll respawn with still no ammo. Flying to the tower won't fix that, but the gunsmith there sells ammo refills which do.
You play one of three character classes, Titan, Hunter, or Warlock, a weird mix of SciFi and Fantasy. I'd love to tell you what the difference between the classes is, but I can't. Because if you start a new character and play him through the intro up to level 2 and the Tower, the three classes play pretty much the same. You attack is determined by your weapon, which is the same in the intro for the three classes. There are differences in the stats, the grenade, and the melee attack, but these differences are small compared to a MMORPG, where you would expect a warrior and a warlock to play very differently. When gaining levels, you gain class abilities, so later there is presumably more difference between the classes, but I didn't play several classes to higher level to find out.
Combat plays mostly like in a shooter game, but with a weird system for weapons: Unlike in a MMORPG, a higher level weapon does not necessarily deal more damage. Instead the weapon has an attack value, which basically determines up to what level of enemies you can damage with it. How much damage it deals is determined by the weapon's impact stat. So if you exchange a low attack value, high impact weapon for a high attack value, low impact weapon, you will do *less* damage to lower level enemies, and only starting from a certain enemy level the change makes sense. This also explains why you can get high level weapons by doing low level missions: The higher level of the weapon doesn't really make a difference in a low level mission. There are weapons with low impact and high fire rate, and vice versa. It might be just me, but I think the high impact weapons are better, because enemies move very fast into cover and thus you don't necessarily always have the opportunity to spray them with many bullets. A boss mob with a regenerating shield can be a tough nut to crack with a machine pistol, but get one-shotted by a sniper rifle headshot.
Destiny's biggest weakness is it's limits to interacting with strangers. In the open world you kind of auto-group with anybody close to you. But in the darkness zones of the story missions you are alone unless you invite up to two other people into your fireteam. Which only works well if these people are already on your friends list. As there is not keyboard there is no typed chat, and the voice chat only works inside a fireteam, so you can't use it to find a team either. Fortunately the strike missions don't have that problem, there you'll automatically be grouped with other random players if you didn't bring your own friends.
Overall Destiny isn't the world's best shooter, nor the world's best MMORPG. But the weird hybrid kind of works, so it isn't a bad game either. One certainly can have hours of fun with it, even if one isn't an expert in console shooters. Having hit level 10 in less than one weekend, of a level cap of 20, Destiny apparently follows the MMORPG convention of short leveling, long endgame. And I can't say yet how engaging that is going to be. As neither "raids" nor PvP interest me much, I might not even play the endgame very much.