Biggest issue for me was that enemies NEVER got more complex than "shoot them until they die", with an added mix of "shoot them in the head so they die faster". I know that's how the original 2.5D FPSs rolled, but it's annoying that facing super uber mecha walking death machines, and there's no way around them besides dual-wielding the AR and holding down both M1 and M2 until they stop moving. The only bosses that broke the mold were the London Monitor (though forcing players to turtle in the ground from an undodgable attack is boring), and the first phase of Deathhead. The end boss of Old Blood is horrendous for doing this. I was flinging shot after shot into him, I spent nearly a straight two minutes unloading, I was tempted to tab out and look up how to really kill it, then it just died. Jager wasn't terrible, but Jager was easily my favorite part in Old Blood.
I agree that all the guns sounded great and moved good, but the gunplay never felt that dynamic. Enemies dropped like bags of rocks when they died and had no good audio cues. Many enemies were so armored it never felt like they were taking any damage. The ARs and the double-barreled shotgun were the only truly satisfying weapons, but the novelty of the ARs wears out real quick and the DB shotgun is utilized two times in New Order and not until the end of Old Blood. The automatic shotguns are so guilty of this. HOW CAN YOU MAKE DUAL-WIELDING AUTOMATIC SHOTGUNS FLIMSY AND BORING?
A general lack of a good arsenal. A pistol, an assault rifle, a shotgun, the cool laser rifle, that weird plasma marksman rifle, and the knife, and a pickup MG. Old Blood picked up the ball a bit with a sniper rifle and a grenade launcher. You spent easily 80% of the game with your view occupied by the AR - the other 15% was the suppressed pistol in stealth and 5% for everything else. Especially pronounced with how stale the gunplay gets.
Perks were fun but usually shoehorned you into unfun playstyles. Killing people with akimbo, a certain way in stealth, and scavenging for ammo are fine ideas. Killing from cover forced you to shoot from cover (ABSURDLY BORING) and killing three people with one grenade is so unlikely, given the circumstances and the relative rarity of grenades.