Last Light is fucking fantastic. I can't recommend it enough, if you haven't seen this already
2033 is a bit clunkier on the gameplay but it's a lovely dark story to play through. I would play the Redux version of the games as 2033 was updated to LL's levels of details and both have the latest support from 4A on XBone/PS4/PC (as well as all the minor DLC material that LL had for Preorders), but I've already bought them for my Xbox...then the original PC versions...and the books...
LL can be played straight away as it fills you in with some of the background (2033), but do try and get it, it's probably worth pennies now. Both games reward exploration, and the story is linear so you don't have to worry about getting too deviated from the missions.
I can't say for 2033's stealth mechanics, but it is possible in LL to kill almost no humans except in the "boss" battles - and even then you have a final choice for most. Ranger Hardcore mode removes the HUD and is recommended that you use that as a re-playthrough, and over a few days, as otherwise you'll come back to a save weeks/months later and forget what the controls are like I did.