1. Variety of weapons.
You might think Warframe just has reskinned weapons that do the same as any other, but that's simply not true. Every melee, secondary and primary weapon have different mechanics. Some of them are shotguns, some of them are rifles, some of them are... lasers. Then there are stealthy weapons like bows. And every single one of those rifles and shotguns and lasers have a different way of killing the enemy. One of them shoots bolts that take some time to reach the enemy but deal high damage, and another one fires intensely hot shrapnel that ricochets! While most of the melee weapons are just swinging, some of them have different speeds and damage. One of them even has an attached shotgun!
2. Variety of enemies.
There are different types of enemies in the game, such as the Grineer, who have armor so bullets deal less damage to them, or the Corpus, who have shields that act as bullet sponges until their real health is revealed, then there is the Infested, who are pure flesh and pretty much zombie forms of the Corpus and Grineer. There are more bizzare enemies out there, such as the Orokin, but I don't want to spoil too much :)
3. Variety of damage.
Yup, there are damage types too. The primary ones are Puncture, effective against Grineer enemies and reduces their damage, then comes Impact, effective against Corpus enemies and reducing their shields, then there is theoretically the best damage type, Slash. This one goes straight for the flesh, being extremely useful against Corpus and even Grineer if you figure out a way to reduce their armor. The Slash effect deals overtime damage to health, so you can just sit behind cover while your enemy slowly dies. There are also elemental damage types, be it fire or electricity. Some special types need 2 elementals to be combined. They are also effective against certain enemies, like Corrosive for getting rid of Grineer armor and Magnetic for massively reducing Corpus shields. Then there's Gas, a toxic cloud dealing damage to enemies overtime. Infested don't like to play around fire.
4. Variety of missions, planets, quests, etc.
SO MANY OF THEM! There are 18 accessible places that have each different layouts and missions. Earth, you being in a grassy layout against Frontier Grineer, or Mars, you being in a desert looking place facing Arid Grineer, or Venus, that surprisingly looks cold (you'll find out why with lore) and is full of Corpus robots and enemies. Then there are planets that take place in enemy ships, there being some beautiful views from the windows. There are also mission types, such as Exterminate, where you need to kill a certain amount of enemies then head for extraction (where you end the mission), or Capture, where you need to capture an enemy by shooting him until he's down. Then there are quests, some really interesting and fun pieces of information. There are so far 3 cinematic quests that reveal a LOT and unlock special abilities.
5. Variety of killing :)
There are these things called mods, that act like a perk for a weapon. There are a LOT of them, some of them reducing your gunshot noise, increasing your damage, adding elemental damage, increasing zoom-in range, increasing reload speed, increasing fire-rate and so on. You can get mods from pretty much anywhere, like enemies, completing missions, trading. To install mods on your weapon/warframe, you need to get capacity, and you can get capacity by leveling your stuff by earning affinity from killing enemies. There are so many builds out there, some of them are designed to mow down Grineer enemies, some of them for Corpus.
6. Variety of abilities.
A Warframe is the armor you play in, and man can it do some interesting things. Each one of them have different abilities (1,2,3,4), some of them do an AoE (area of effect) blast of damage, other ones deal extreme damage to a single enemy, one of them even makes you invincible! Then there are passives, always active when you're playing on a certain warframe, such as Ash, making Slash damage procs last longer and deal more damage, or Banshee, making all types of weapons silent with no use of mods.
Long story short, it's a great game. It's very addicting and it will get you hooked instantly. I haven't even began to explain what platinum is, what it does, because this game is huge! The graphics are wonderful, the mechanics are unique, and it's definitely worth your time. Come on, it's free to play! Try it!
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