OP, both of those games look damn fun, especially Shattered Horizon, but I guess games die.
Battlefield: Bad Company 2. I invested so much time into this game on my 360, but it is a huge shame that the game pretty much up and died after Battlefield 3 came out. Last I checked, the game is populated almost exclusively by a small amount of level 50s, and that was about 2 years ago. I got it on my PC, and it was great to go back, but something just isnt right, but I cant pinpoint it.
Mass Effect 3 Multiplayer. A shadow of it's former self. It was a feature that nobody wanted, and it was implemented poorly, but my god it was a good time with 4 players. If the Dragon Age: Inquisition multiplayer is anywhere near as good as ME3s, then I can imagine sinking a very large amount of time into it.
Space Marine. I got it a few months after it's release for about £15 including all of the DLC, however, little did I know that if I wanted any chance at playing the game's multiplayer, I would have to play the vanilla version because the DLC playlists were dead. I think that I played one single game of the dreadnought mode, and I never found a server afterwards. It was super fun to jump across the map as an assault marine, or hunker down and open fire as a devastator, but I guess that Space Marine was just not as popular as I would have hoped.