This maybe a bit early but potentially Street Fighter V. I don't think it outright killed SF. It has damaged it however. Granted the game plays very good but the DLC bullshit and the always online thing. Botched launch. It has a bad reputation that has affected it's ratings even on amazon plus with in a few months was reduced to 20 bucks. The SFV collectors edition was quickly reduced to 40 bucks.
Mortal Kombat vs DC. Ok yes Mortal Kombat still lives but under a different company. This game was desperate to get that Marvel Vs Capcom but nerfed the MK characters. Such a mistake. It helped kill Midway.
Dungeon Siege III. Here is a series once held in the same regard as Diablo and in some ways bested Diablo. With III they made a unbalanced bland game trying to cash in on Dragon Age half assed Dialogue Trees that don't affect anything. Bosses that are all the same and re skinned but act the same. They are also heavily unbalanced and difficult..they are designed for you to have online friends play with you so if Solo..sucks to be you. It is playable and for mega cheap is a just ok fix for Diablo but so many better options. Series is very likely dead.
