I will give you a short introduction to DnD.
There are several types of weapons and armor. Each type has a base value of stats as written in the rules. For example every longsword has 1d8 slash damage which means it causes 1-8 points of damage, plus some other bonus damage for example from having high strengh.
Every char should be profient with the type of weapon and armor they are using, which depends on his class, race and feats. A human wizard won´t hit anything with a sword and cannot cast spells when wearing armor. Better give him a staff and a robe. A fighter can use almost any kind of weapon or armor for example.
In the beginning you can get a generic weapon of almost every type. Later you find a generic magic weapon like a longsword+1. It has a higher hit chance ( +5%, unless the enemy armor class or your own attack bonus is extremely high or low) and deals one additional point of damage, so its 2-9 points. Some enemies are resistent or immun to some kind of damage so you need magic weapons against some enemies.
When exploring dungeons or beating bosses you can find artifacts, equipment with unique magic abilities. Some famous examples from BG2 are celestrial fury (Katana+3, high chance to stunn enemies on hit), mace of disruption (high chance to destroy undead on hit) and the holy avenger ( greatsword+5, user gets resistence to magic, dispells enemy magic effects on hit, can only be used by paladins).
In general, magic items are rare (at least in the beginning) and artifacts are very rare. Each artifact is hand crafted, hand placed and has unique abilities.
DnD tries to keep the numbers low and each magic item you find should feel meaningful and make sense. ( does not always work)
There are no random items, so you will probably not find a sword that increases bow skill or an axe that raises you intelligence unless thre is a good reason for it.
I prefer the DnD system over D:OS any time.
In D:OS2 all items felt meaningless because it was totally random and you will find something better some minutes later.
Diablo was very boring for me, you fight random enemies in random places to get random items.
I rather find the holy avenger after beating the red dragon at the end of a huge dungeon and use it for the rest of the game.
Prof. Dr. Dr. Mad S. Tist 
