Here is your second cardinal sin. Not explicating your game stats in the bloody game itself. [...] if I get an item that boosts a stat by X amount, kindly explain to me in very basic terms what that entails in practice. What the hell is 'Heroic Defence'? What's the benefit of 'Intelligence'? How does 'Magical Attack' work? Don't make me go and look it up on a third-party website. Let me find out by mousing over, or at the very least, by clicking on a Help button.
This goes way beyond MMOs (of which I have little experience, but since we're piling on...)
I really quite enjoyed SW:KOTOR, despite it being totally not my preferred game genre.
But. Not being a tabletop RPG-er, I didn't have the faintest clue about how the D20 system works. The closest I ever got was playing AD&D about 20 years ago, with a GM who did a good job of shielding the nuts-and-bolts of the mechanics from the players. As a result, I basically had to go around and re-do the first third of the game, when it became clear that most of my early level-up decisions were complete garbage, and I discovered I now had a character who was completely, radically, unsuitable for my playstyle, and I was getting twatted in the most trivial combat encounters, even after turning the difficulty way down. Second time around, I still wasn't great at figuring out how these numbers fitted together, but I stood a chance, at least.
Elsewhere, I basically abandoned a promising (if very, very, nerdy-looking) hex-based computer wargame unplayed when it became clear that my only chance of playing it in a meaningful way was to inhale a copy of "Jane's Armoured Fighting Vehicles Of WW2" first. Then, at least, I'd know which tanks to use against infantry, which against non-armoured vehicles, and which against other tanks, which might let me live long enough to figure out what all the different infantry units do. As it was, I tried to repeat the whole "Germany invades Poland with a bajillion tanks in 1939" thang and got my ass handed to me on a plate by three guys armed with pointy sticks, some of them on horses, because those tanks just bounce off entrenched infantry, and these are useless against any vehicle with more combat capability than a bicycle.
This is why I always preferred SF-based wargames (even in the tabletop arena) over historical - the SF ones *know* that they've got to explain to the players which units are good for what, but most historical ones assume that the player already knows the difference between Panzer II/III/IVs.
 Still Don't.
 Within reason, I regard this as a Good Thing with an RP group who were far more interested in the "group storytelling dungeon mosh" angle than Rules Lawyering or Meticulous Table-Studying.
 If it were planes, it would have been a slightly different story - I have enough of a clue there to survive long enough to figure the rest out - but tanks/half-tracks/etc? No chance.