- Son of a Gun was bugged and didn't actually give any +damage for pistols. However the speed system was different so it was qutie easy to get a pistol to have 0,1 fire time.
- Mods worked differently and allowed you to place virtually limitless mods on an advanced weapon. I once had a 2d12 pistol for example.
Nothing more i can remember except using the unload bug to load weapons over their maximum. This made all shot reload weapons extremely powerful. This was cheating ofc.
All of that because of bugs. # 2 and #3 were fixed quite fast, while the first was in game for several versions, until Kornel found out that actually damage bonus is not working. SoaB didn't gave bonus too. It was the trait with no effect.
Rockets - they were ok. Then were the buggy system of dealing damages from explosion. IIRC, rocket's damage was dealt twice.
About rez-killing on Nightmare - it was very difficult on deep levels in that time. Because of no "powerups doubled" bonus, because of SoaB that wasn't working, because of no Triggerhappy. It was possible to scum enough exp from demons and chaingunners on level 2 to get HR, IM and TaN to just run through deeper levels - it was the most possible way to win, but it was very hard to survive somehow long on later levels with all of that resurrecting tough monsters.
Game balance sometimes was changed dramatically from version to version and most of the changes i even don't remember. Better to check version history, or even download an old build and try to play it.) v.0.9.8, or v.0.9.8.5, for example.
Edit: Yaay, my 666-th post!