It really is important to play the main game first or at least start it and get into it a good ways before trying the DLC as the DLC just throws you right in with the xeno or visa versa lol with no introduction or lead up. Making sure you start with the main game helps establish to the player what the rules are or what to expect.
I remember the first time experiencing the beginning when you get that cutscene that shows you there's something wrong, then the music comes and ramps while you are waiting for the tram. Good grief. I didn't know what I'd gotten myself into or what to do. I got into the tram and immediately turned around because in most games the control panel is right next to the opened door lol but it wasn't there. I finally realized it was in the back and made my way there. I don't think the button worked or I pressed it and it was too late and think I looked back once to see if I could get a glance of whatever was coming. I turned around and just crouched in the corner hiding my head while thinking "please no, please no, please no" and it grabbed me from behind and either spiked me or face punched me, I can't really remember.
If anyone needs any tips let me know and I'll be happy to share. I really liked the way the game was paced too. There were some surprise missions and there were nice moments of reprieve from the Alien woven in and out of the game's progression.
There's times where its just you to let you breath easy and other times with just humans and/or synthetics.
That helps alleviate overall stress for the player.
Also, I did not find this until after I finished the main game and started the dlc, but there is a really nice anti-aliasing mod listed on Steam for the game. The game looks great but it has pretty rough aliasing in areas of the environment(especially around light sources) that are pretty noticeable. Most of the time these solutions seem to be hit or miss or even artificial, almost placebo-like however, this mod actually works and is amazing. It completely kills all that aliasing using some sort of temporal anti-aliasing method and its really outstanding. I noticed little to no performance impact and the result is just crazy. Makes those sterile space station environments look even cleaner and more crisp.