I've been wearing Teva Terra Fi sandles since the original and have had every model. Terra Fi 1-3 were all very similar with a few subtle style and performance changes. The Terra Fi 4, in my opinion, is very different than previous models. It has a much heavier sole similar to the Vibram found on Chacos. The webbing is pretty much the same but the fit is different to me. They run a little smaller but not enough that I needed a bigger size. If you are a Terra Fi fan you'll probably like this version, but you may want to check out the new lite version as it may be more similar in weight and fit to the older models that your used to. Over all it seems like a more stable and durable shoe than previous models, which, for me anyways, is not a bad thing.