You've done all that in 10 hours? What's the longevity of Brink?
Starting at midnight (PC/Steam Preload) I played till maybe 3:30am before packing it in for the night, lol. I just couldn't pull myself away because I'd see another map count down...
As for the longevity, in my opinion that depends. Are you going for all of the achievements? Leaderboard spot? High level/badass looking character? Or are you going to just play with your friends?
I'd say that it'd be more beneficial anyways to get a good team of friends together to join your game to go through the first 3 campaign missions, then attempt some challenges to unlock weapon mods and weaponry while gaining xp in the process. I plan on doing some two star challenges before I start to do the Security campaign tonight.
Also, if you're a svcker for a good story, you should actually LISTEN to the audiologs you unlock over your playthrough. Just my two cents

Also at the end of the Resistance campaign...
Spoiler One of the rewards was a Movie log, similar to an audio log but cinematic and EPIC.