Depends. You have some natural advantages and disadvantages from class to class, but mostly you have this huge advantage when playing paladins, rogues or frost mages. By far, rogue is the best, with a ridiculous combo of offensive and defensive spells. Paladins just have lots of defensive spells, and frost mages are effing fast casters with the best instant casts.
Also, how you assemble your gear will have a direct influence on your gameplay and efficiency. Its not like UO where you can just cap every properties availible.
Being that said, everything else is skill based. Knowing when to interrupt spell casting, when to stun, when to run, when to use this skill or that. There is some luck involved in critical strikes, dogding, parrying, blocking, miss... Those common RPG aspects.
Also, as said, depending on how you stack your properties, you'll be required to play differently. Stacking haste on a meele means that you need to stay in constant meele range, so you can maximize damage. Stacking Critical Chance will make your game less luck-friendly, but you'll get everything else weaker, slower, and so on.
Well, as i said way before, it gets pretty boring to PvM. PvPing is the only choice you have to have some fun after sometime (besides friends and guildies in vent joking around all the time).
