To go through to the next act you don't have to fulfill all the quests but there is a bug in the first episode. I had already finished one of the quests when I met a NPC which advised me how to handle it. Concerning the other negative aspects, I must point that there is no multiplayer in Archangel which will seriously affect it's life time. There is no map also. Even if the levels are somehow linear (the quest order can differ a little bit) you feel sometimes disoriented, you cannot find the point of you departure or the one where you have to get. A very good example is the cave of the seven seals where I spent a few hours because of its architecture. The producers implemented a few secret locations and if you find them the reward will be great. The fact is that sometimes you will have to find them to this can be a hard task for the ones who don't pay too much attention to details or who want to finish this game in a very short period of time.