- Difficulty-wise, Normal is as advertised but gets fairly easy once you're fully kitted out. Hardcore might be better for a veteran Metro player, but it does start out very rough for the first few hours. Ranger Hardcore is likely best left for New Game+ which allows you to preserve your weapons and upgrades from the previous playthrough.
- Like in the previous games there is a hidden morality system that decides which ending you get. For the good ending help people, don't kill people who aren't obvious bad guys (red reticle), knock out the others (yellow reticle) when necessary and remain stealthy for as long as possible.
- Besides this morality system there are also various factors that decide what happens to some of your squadmates. You may want to read a guide for this, but the basics are - don't fight neutrals (non-bandit locals, highlighted in yellow when you aim at them). If possible, stealth right past them without knocking them out or getting shot at. If not possible, at least knock them out instead of killing them.
- Many main-story stealth sections are based around advancing as far as you can without being detected to trigger a conversation that will make the enemies move on to more convenient spots.
- NOT trying to knock everyone out makes some stealth missions as lot easier.
- Enemy armor isn't just for show - it can block a bullet or thrown knife. However, hitting the parts that aren't covered by armor still works, and every humanoid enemy with the exception of minigun soldiers can be knocked out up close.
- The minigun really is that useless in Artyom's hands.
- After leaving the underground base in the desert level, sleep in the first resting spot you encounter (the elevated one). A fairly major bit of story is randomly hidden there.
- Starting a New Game+ breaks a lot of "kill x enemies in fashion y" achievements. If you want to get those, I'd recommend replaying specific chapters.
- NPCs are incredibly chatty and will talk forever. Listening to them is a big part of the game, you won't be constantly shooting.
- You can use your binoculars to scout out points of interest on the map (focus until the location you're looking at "sharpens" by loading in with more detail). They will initially show up as question marks. Some of them will simply be a monster nest with one or two bodies that can be looted. It's not always worthwhile to clear out these nests just to get some scrap and the appropriate icon on the map.
- Counterpoint - about 50% of monster nests have a weapon mod lying around, which may prove quite useful.
- Being out in the world will get your weapon dirty, especially when you dive into the water. Very dirty weapons will jam, especially the rapid fire guns. When you are exploring (and rarely shooting) it is best to hold out a weapon that you won't mind getting dirty (probably the Tikhar).
- The Tikhar rifle is pretty annoying until the quartermaster gives you the airtight pneumatic system upgrade. This will allow you to preserve gas pressure, even if you are not using the rifle.
- The Tikhar's explosive bullets (gained at the start of the desert level, TAB+R to switch ammo) annihilate spiders.
- The Taiga chapter has a boss fight at two points. The first time is supposed to be a challenge, but can be skipped. Use a molotov cocktail on the boss (you can find some of those nearby) and then use the rope next to the gate while he is distracted by the fire.