Zen looks to be promising from what I've seen, although I cannot prove that my sources are 100% accurate.
But what I can prove is that AMD claims a 40% increase in IPC over the current FX series. This means that if you have an 8350 at a constant clock of 4.0GHz, and a Zen CPU at 4.0GHz as well, the Zen CPU will (theoretically) get a 40% higher score in single threaded tasks. I say single threaded (and not single core) because new Zen CPUs will have Simultaneous Multi Threading, which means that they may be able to compete with the multi threading solution that Intel currently is using.
Also, we all know that many AMD CPUs are cheaper than Intel ones. I heard that there will be a 16 core Zen CPU with SMT (32 threads) at undisclosed clock speed that will theoretically compete with the 18 core Intel Xeon CPUs out there.
Now if AMD can keep their pricing reasonable, then the increased IPC will get the attention of gamers, the 16 core chips will get the attention of video editors and CAD engineers, and the (unconfirmed) 32 core chips will get the attention of people running server farms. I think I will also wait for Zen before I do my next build. I want to see what the price is for something that competes with the 6700k.