Took them out on a 4 mile run yesterday and while it's not dramatically different from the 2, if you liked the 2, there's a good chance you'll like the 3 even more.
Pros (so far): More and softer Lightstrike Pro, forefoot geometry feels a little more propulsive (possibly a lot more propulsive for people who are legit fast), increased stability due to wider midsole and (probably) the re-designed carbon rods
Cons (so far): Like the Takumi Sen 8, the upper feels kinda crude compared to their peers both in terms of the preciseness of the fit and comfort/materials. The 3 fits similar to the 2, but I think the heel area is a little more dialed in and the toebox is a little more accommodating width-wise, but also feels more shallow than the 2, though this might be because the 3 has an overlay over the toebox to the tip of the shoe that the 2 doesn't have. On my right shoe, the overlay would sometimes pinch the top of my right big toe on toe-off. Hopefully it'll go away as the upper breaks in, or it's gonna be annoying.