A lot of people are simply selling this game short with comparisons. I've heard comparisons to Halo, Call of Duty, Titanfall, Shadowrun, Borderlands, Skryim, and WOW. In some ways, those comparisons are accurate. Destiny takes a lot of little elements from other games. Ultimately though it feels very unique and I honestly think it's good enough to be GOTY material.
It doesn't just slap ideas together. It takes and builds on ideas from other games. For example, Destiny has a loot system similar to Diablo or Borderlands where guns are listed in tiers. However, unlike Borderlands, Destiny has a pretty in depth upgrade system which include choices similar to COD's attachment system (scopes, barrel types, ect). You have armor pieces which are both cosmetic as well as have attributes attached to them...these can also be upgraded. You can unlock shaders which are basically camos. Higher level gear has been mostly locked in the alpha, but each tier appears to allow for more upgrades.
The PVP feels pretty fast paced, and the slightly longer killtimes makes camping less effective. There is no view kick or flinch in gunfights so gunskill comes down to your ability to control the recoil. The jump abilities are unique to each class and each can be upgraded several ways to enhance it to your playstyle. We have only seen two maps and one gametypes. The gametype is a fusion of TDM and Domination. One of the maps had combat vehicles and MG turrets, while the other was just players vs players. On the vehicle map you can always call in your non combat vehicle at any time if you want to get somewhere fast.
They kept the idea of power weapons from Halo through ammo drops. When you bring your Heavy weapons into PVP you will have zero ammo. Ammo is relayed in static drops which a player must then acquire as a map pickup. If you die the heavy ammo is dropped from your body for someone to pick up. Special/secondary ammo is limited and also acquired in drops, but stays with you through death. However, if you change your secondary weapon mid game you will lose your current ammo. Only the primary ammo refreshes upon death. You have super abilities which slowly refill (very slow), but streaks will fill them up much faster.
Here's an example of PVP from a MLG Halo player:
Besides PVP, there will be end game content like Strikes and Raids. Strikes are meant to take about 30 minutes to complete and are mini dungeons with bosses. Raids will be insane end game content with more dynamic elements and much harder AI than Strikes. Bungie has said it took their playtest team 16 hours to complete one. For people who are only interested in campaign...it is there. It will have cutscenes and our character will be shown with all its customized armor and looks.
When exploring in free roam mode there will be times you encounter enemies far higher level than you. Also, there are hidden caves which might be hidden in dark spots or require you to jump off a ramp to reach. It does have a bit of a Skyrim feeling at times with the depth of exploration. The alpha has only shown one location on Earth (and some of it is blocked off). The final game will span four planets each having multiple locations. It's just insane how big this game will be when it comes out. I really can not wait.