In SAO there were a lot of things that the novels did a better job of explaining: like how many players were actually playing the game, and how many were sitting around in the first floor. And things like the tournament style PvP fight Kirito had with Heathcliff is better explained in the novels. Since SAO was fairly dead in terms of population (6,000 players is a super low number for an MMO that size) it was a little bit off-putting to see a packed arena. But in the novels it explains that every time a floor is cleared, tons of players come up there to have a floor clearing celebration, and that floor 74 was the first floor that had a roman style arena so people were excited to see it in action.

The novels also better explain the very end when Kirito fights Heathcliff again, he gets goaded into using a sword skill and knows at that point that he'll die because there's a slight pause at the end of it where he would be open to an attack. The anime shows this, but it's also kind of confusing like "why would Kirito give up when he looks like he's winning?"

Anyways SAO has a bunch of little nitpicky things like that. ALO also has some similar things, but I actually find it a lot more faithful than the SAO arc was in general.