My two cents in the Destiny vs Warframe debate...
Destiny is basically paying 150 bucks for a story driven, 35 ish Hours game where you constantly repeat the exact same missions over and over again to grind better guns and hit max level... It has three different classes , which are basically identical in most regards (grenade, melee , hover jump and a super). The endgame consists essentially of grinding the same raids over and over again to get the drops you want, to repeat the same story mission and strikes every day/week as work-like chore, then repeating the same bounties over and over again so you can level up your new guns. Weapon variety is bad, as there are only a handful of weapon "families", and every weapon in a weapon family behave roughly the same. Clans serve no purpose, as the game does not offer anything cool to people in clans. After the 30ish honeymoon with this game is over, all that's left to accomplish is to grind your way to acquiring all exotics and maxed level gear, but only 6 or so weapons are really must own anyway, and you can only wear one exotic gun at a time anyway...
In contrast, Warframe is basically a Free 300 to 600 hours space ninja universe, in the sense where one player can experience eveything this game has to offer without paying a cent. Granted, most people that get into Warframe end up paying 60-100ish bucks average, mostly because character and weapon slots expansions cost platinum, and unless you feel like trading duplicate prime parts and mods for your platinum, it's much easyer to spend a little money once and avoid that tedium. Still, it's possible to do good in Warframe without spending a single buck... As pretty much everything can be gotten without spending money, or with a little trading, if need be.
In terms of gameplay, Warframe has a random level generator system that creates new experience every time you do a mission. This works imho much better than repeating the same story mission over and over again, like in Destiny. The scope of Warframe is also much bigger, with a whole solar system filled with missions to clear. The game always has things to do, including timed alerts, invasions, infestations, syndicate missions, events, solar rails takeover, synthesis scans and codex scans. The game offers alot of endgame content in the form of orokin void keys, orokin derelict keys, and recently, the inclusion of raids. You play Warframe because you want to try the new frames, the new weapons, and so on.
In terms of gameplay, the game offers a whopping 23 different frames, each with 4 unique abilities that change their playstyle tremendously. In terms of weapon, in comparaison to destiny, this game offer like two hundred different weapons , each with their unique traits and behaviour, including proper melee weapons (none of that "use a sword for 30 seconds before it dissapears crap"). Weapon variety is awesome, you can use pretty much anything you can think of, from bows to exploding trap throwing stars, from ice beam guns to strange guns that shoot squares, from Katanas to wolverine claws, the list goes on and on and on... Warframe goes above in beyond what is usually avialable in games like this. Then there's the modding system, which allows full customisation of your frame, your guns and your melee weapons. You get companions, kubrows, syndicate mods that change the way your skills operate. Remember how Destiny's ships are just loading screen skins ... In Warframe, you board your ship between every mission.. And you can fly in space using Archwings too ! Finally, there's the clan / alliance system... Allowing you to basically building a gigantic, fully customisable dojo for you and your clanmates, to develop unique clan weapons and frames, to build solar rails and to take over dark sectors located in the universe... So much content... And I feel that's just scratiching the surface... I'm not even talking about the parkour, the awesome mobility of the frames, the fact that melee is a viable tactic to complete missions, the fact you can have steath frames that can complete missions without being spotted, the list goes on and on and on...