Napoli are playing very well, and it's no coincidence that they're in first place. The interesting thing is that Lukaku isn't missed, as Antonio Conte has managed to replace him admirably; in fact, the team is scoring goals without any problems.
All in all, it's going very well.
Playing four matches and collecting twelve points is no coincidence, but rather the coach's excellent preparation. Although their Champions League performance was a bit disappointing after their defeat to Manchester City, Napoli's overall strength is much stronger because they have a number of experienced players, and now it's up to the coach to combine the strengths of his players.
The upcoming match will be a bit more difficult and challenging, as Napoli will face AC Milan, and the match will be at AC Milan's home ground, making things a bit more difficult for Napoli. A defeat could impact their standings, as Juventus will face a much easier opponent in the next match.