Arteta has done well considering the mess he inherited and the squad at his disposal. However, even with all the good work this will turn out to be a huge missed opportunity for Arsenal. There are similarities to Emery's first season in which Arsenal actually had a very good season but faltered at the end. And with that just like after Emery first season, they will drift further and further away from CL spot contention.
If it wasn't the case already, Arsenal's time as a top club is officially over. With the rise of Newcastle (ironic considering today's match), West Ham etc, I think we could very well see Arsenal become a permanent midtable side within the next few years or so. And in the Premier League that is not a safe position to occupy.