I'd say it was very much like most of Arsenal's league perfomances at the end of last season: not always fluent, sometimes living on the edge, but grafting hard and always finding just enough quality (and/or luck) to get the desired result. Really, either team could have won the match, but Marseille couldn't take advantage of the few openings presented to them - notably when Fanni yanked a close-range volley just wide early in the second half, and then later when a horrible mix-up between Szczesny and Mertesacker (vaguely reminiscent of Koscielny in the League Cup final vs. Birmingham) was cleared off the line by Gibbs. On the other hand, when Marseille made their mistakes in the second half, Arsenal punished them: Walcott had looked peripheral all night, again, before volleying home a great goal which will hopefully give him a confidence boost he rather needs, and then Ramsey took advantage of a huge gap in the Marseilles defense and then got a lucky deflection off of a defender's boot on his shot. (That goal fits the Ramsey-as-emerging-superstar narrative more than it creates it; he made a good run, but I wouldn't call it a superb piece of talent.)
I don't think Arsenal could have complained with a draw, but as much as I've hated hearing Wenger prattle on about "mental toughness" in recent years - hoping that the wish would father the deed - this team does seem to have more self-belief than any other Arsenal squad of the last five or six years.
