I completly enjoy this game and reccomend it to anyone that likes futuristic shooters.
It has great gamemodes similar to Call Of Duty, Battlefield, etc.
It's a shame that no one is on Multiplayer anymore, because it is a masterpiece, but no one notices it, it runs well on most system and requires DirectX9, not like Retribution where you need DirectX11.
This isn't a Pay2Win game like Retribution, you earn things and keep them by leveling up. Not by constantly paying for Zen. You don't keep things you earn unless you buy them with Credits in-game, or real money. There is no currency or anything in Tango Down. And it's easier to level up than pay real money for guns and things in Retribution.
There is more things in Retribution to try, but I do wish it focuses more on the "F2P" method, Tango Down's only $0.99 on the Store, so it's fine for your wallet. The core gameplay of Tango Down is more fun than the gadgets in Retribution.
The servers in Tango Down are always up and running. Not like Retribution, you need to connect to Europe to play on public servers, and even private servers.
I think this game deserves more attention than Retribution, but it's only my opinion.