Completed my 1999 run and I must say I was disappointed. For the entire game I was waiting for it to get challenging, but it never did. Only died five or six times total.
For most of the game I ran with a sniper rifle and shotgun, using Possession to take out key targets and Bucking Bronco for crowd control if enemies somehow managed to get close. I always end up sniping in games like this and I was hoping that 1999 mode would force me to take a more active approach to combat, but most of the time there are just too many safe places to snipe from, ammo is plentiful even without using vendors and the AI can't do a thing to smoke you out. Once I got and upgraded Return to Sender and equipped Blood to Salts, what little challenge the game offered just flew out the window since I could just walk up to enemies and shotgun/hand cannon them in the face while blocking everything. Even completed the final battle on my first try using only shotgun, hand cannon, Return to Sender and Possession.
Granted, there are a few fights in the game that forced me to take a different approach. The first handyman fight ended up being the hardest fight in the game since the area has no skylines, but running around and possessing the two turrets got him down eventually. I was expecting the
fights to provide some real challenge since I initially had some trouble with them on hard, but they were a joke with Shotgun/Charge/Burning Halo/Brittle Skinned.
I think the main problem is that the game just provides too much ammo and salts. There was never a point where I felt like I was low on either, even though I was using the same two or three weapons the entire time. Meanwhile Return to Sender and plentiful salts make you effectively invincible, which removes all tensions from the combat.
Don't get me wrong, I still enjoyed the game, easily my game of the year so far, but I just wish it had provided some actual challenge.