Just bought my copy of Borderlands so I can finally play it at home instead of at my cousin's house. I'm not sure which class to play as, but my last character was Mordecai.
What are the core gameplay differences between each class?
If you're playing by yourself, I'd suggest Lilith, because she's so overpowered and fun to play that it at least somewhat makes up for the otherwise not very fun singleplayer. Otherwise, you can check the Borderlands wiki to see each character's available skills. The class mods available for each character try to make you focus on specific weapon classes- SMGs for Lilith, Snipers and Pistols for Mordecai, Assault Rifles for Roland, and I
think rocket launchers for Brick. You can obviously use all guns on all characters but if you want to specialize in a specific type of weapon, then there's a character that goes along with it.