For me, Arena mode can't decide what it wants to be. All my matches lasted as long or longer than an other CP/PL match I might engage in, and I don't think thats what Arena is suppose to do. Yea sure Rounds are real short, but with 5-in-a-row people don't seem to "push" it until 3 or 4 , thus restarting the whole thing. It's kind of self-refuting.
I think more than anything else the "world" additions in this update are pretty daring and good starts for new opportunities in TF2 play. Though, I'd agree that something feels missing.