What about having Monster Essence Shards instead of gems put into sockets on items? Basically, like in most games, each item in the game would have sockets. Each item would start with 0 sockets, but there would be an npc that could add up to 4 sockets to each item for gold. The 1st socket would be cheap, but adding the 2nd, 3rd and 4th to each item would be quite expensive. It could also require some PvE points, and perhaps a Boss type resource.
Each monster in the game would drop its very own essence shard at a very low % chance. Probably around 1% drop chance. This shard would give a special effect to the item it is socketed into. You could only have one shard of each type. If you had e.g 2 Polar Bear Essence Shards in your items, you would only gain effect of one and the other one would be disabled. This way if there are 12 items slots, each with up to 4 sockets, it gives us 48 sockets to fill with 48 different shards. This further gives each player a choice of how they want to build their character.
Mountain Wolf Essence Shard - Increases all physical damage done by 10%
Polar Bear Essence Shard - +20% Max HP
Imp Essence Shard - Increases all fire damage done by 20%
Skeleton Warrior Essence Shard- Decreases all physical damage taken by 10%
Skeleton Mage Essence Shard - Decreases all magical damage taken by 10%
Siren Witch Essence Shard - Decreases all water element damage taken by 10%
Water Elemental Essence Shard - Increases all water damage done by 20%
Goblin Warrior Essence Shard - Gives 33% chance for your auto-attack to hit the second time instantly
Vampire Essence Shard - 7% of damage dealt heals you
Ice Golem Essence Shard - Gives your auto-attack and physical skills 33% chance of slowing down the enemy for 2 seconds by 30%
Goblin Leader Essence Shard - Increases threat generated by you by 33%
Seraphim Essence Shard - Increases damage dealt to Shadow element enemies by 25%
Lich Essence Shard - Changes character's element to Shadow
Dryad Essence Shard - Increases healing provided by you by 25%
The Greater Hag Essence Shard - Increases the duration of all your buffs by 25%
ETC.
These are just basic ideas what these effects could be. But as you can see, they could be anything so there would be an endless possibility of building your character. And even if you met 10 different DPS Paladin classes, each of them could have a totally different playstyle.