Basically, all Diablo games play differently.
Diablo I is an isometric dungeon crawler where management of resources is important in making every decision of your adventure e.g. leaving enough space for Healing potions and Mana potions. In fact, the game was a little unbalanced and unfair to physical combatant classes (Mages were OP and makes it a lot easier to finish the game).
Diablo II was a little less harsh of a punishment in the sense that they want you to weave in non-spell/skill based attacks in between so that the game feels like a nice synergy during combat (this applies to every class). This is exceptionally prevalent with elites that are immune to elements whereby you would have to rely on either physical attacks or make sure your build comes with other means to counteract them.
Diablo III is a lot more streamlined and requires almost no-tactical play and brings out a very fast-paced action type of ARPG with a clusterfudge of balancing that Blizz needs to keep introducing so that every class plays differently yet powerful enough to render interest in us, the players to be invested in playing them.
Basically, if you haven’t played anything before Diablo III, you definitely will not enjoy them in the 2 previous incarnation of the title.