Extending on Heavenfall's comments, here are my 2 Bitcoins worth:

We've reached the point where the in-game factions are becoming ever more richly distinct from each other. This gives you the chance to enjoy some unique play depending on your choice of starting faction. E:WoM fell short here.

Do you want another retread of monsters you may have experienced many times over or would you prefer something fresh? Personally, I like fresh and new.

If you know E:WoM, you will quickly find its DNA in FE. Concepts, principles, back story, lore, i.e. the canon of E:WoM is here and familiar. Beyond that FE is more fun, challenging, thought provoking and promising (as a developing game). For me I see higher replay potential for FE than I experienced for E:WoM.

As Heavenfall noted, only you can truly define "worth it" at this point. Do you like to be served a finished meal and delight at the surprises it contains, or do you enjoy the cooking process where you get to sample and course correct and try out some variety before locking in? Do you trust the particular chefs in the kitchen will ultimately serve you something sumptuous or are you not sure they'll actually deliver? Are you willing to tolerate some frustrations, reversals and denials regarding components of the finished product that are important to you in the hopes of getting a better overall package in the end? Frankly, I think it comes down to you either wait until the game gets released and evaluate multiple reviews prior to investing or else be prepared to invest both your money and your time now to help create a game that you'll enjoy and want to play.

Good luck and good gaming.