Just the weapons. Ideal for those who don't like Hexen's limited weapon set, and this will work with any iwad and pwad that doesn't have custom weapons.
The differences are in the text file, but here's the main ones:
Blue & green stuff spawns where blue used to be, and yellow & red stuff spawns where green used to be. Both give only half the usual amount (rounded) to maintain the balance. (this is the only change present in both mods, the rest are RPG mod only)
Serpent items replace the various Hexen ones, most using shared spawns with equal chance of appearing. (in some cases nothing will spawn, depending on what item it is)
Serpent armour replaces Hexen armour in a similar fashion, but they are grouped in terms of class usage (ie. fighter only, fighter/cleric and all three) so that each class gets the same each time. The exception is dragonskin bracers, the replacement here can be any of the 7 types.
Shopping is handled with an item that you can use once every 30 mins, it teleports you to a shops/holy temple map and leaving this map will take you back to the map you were on before.