Where and when do I find them?

I felt this game was too short, am i the only one???

There were other fairly decent attempts (I'm quite a fan of DOOM III) but this really is the best version of DOOM since OG DOOM. Change my mind. Or agree, whatever suits :)

Ive just finished Doom 3 adn all DLCs. Ive finished the first mission of Doom 2016 and its okay. Im hoping it gets better, does it?

Helping VEGA on the train station, before i go to the next level, i need to fight a crap ton of monsters but i keep dying! Any hints? Ive tried the green gun but only gives 3 bullets, tried the chainsaw for those pesky demon dog bulls that keep charging at you, but a whole gang of monsters attack like crazy. Any hints from you guys????...