I bought the game and all dlc bundled for cheap.
I've beaten everything it has to offer, but I have not done every objective on every level, or beaten safe haven or lost contact more than once. I got to rank 10 on the leaderboards for quickest time on a level called blast seat on pc version.
As I found the game easy, I found all of it's dlc trivially easy. I was more at risk of the game crashing or hard locking my whole computer despite being able to max the settings.
As for your trouble with the game, did you know you can raise the tracker which will show you a green bar that tells you where to go? I finished the main game once on hard without knowing that. Second advice is to throw flares where you want the alien to go. It's basically every bit as useful as the noisemaker, and the preferred way to get distance between you and the alien. Third advice is that you can't go wrong playing as either of the two ripleys (on every level except overrun), as only they start off with the flamethrower. You should not need any med kits for any level accept safe haven and lost contact. If you really are taking health damage it means you're into asphyxiating yourself or getting beat up and thrown around, which says a lot about you.
The reason the alien gets you while in the vents is basically because in there it becomes a charging bull that prefers to go straight through you. I have repelled the creature in the vents before but only with the greatest possible distance between us that the flamer would effect it.
