The Martial Law pack is very useful, you wouldn't regret the purchase but it's not really needed if you feel like you caught on quick enough. And also, you should do your Hardcore run first and then celebrate that achievement by running through Zealot with
your special gift you receive.
the dlc CONTAINS A FEW GUNS AND SUITS which are useful if you find yourself getting stuck, the force gun is in the martial law pack which also contains a suit that gives you +damage to the force gun, which is very useful when attempting a harcore runthrough
as having a fully upgraded force gun is like havin a cheat code. although i bought the supernova pack for my runthrough as it has a suit with +15% health per pack used, which i found more useful, although am still on my hardcore runthrough i have already completed
game and am also halfway through zealot runthrough on new game+. all in all the dlc packs contain about 6-8 guns with 2-3 suits that cn be very useful :) hope this helps
I suggest playing the game BEFORE you buy any dlc. You absolutely don't need any of the weapon packs to beat the game easily. If you are going to buy a weapon pack I suggest the Martial pack strictly for the Force gun.
The dlc "Severed" is focused around a different character. His actions take place around the same time as Isaac's. I suggest playing this AFTER you play through the main game.
Now I see you haven't played the first game. I assume you bought the second game since you posted this on the DS2 forums. Hold off on playing the second one until you play the first one, which is $20 brand new (even cheaper used obviously). If you have
any interest in the story play the first game first. No matter what anyone says YOU WILL be missing out on important details right from the beginning if you start with the second game. If you only care about blowing *** up then it doesn't matter, and shame