We've had SuperNova suits for the past three seasons, and are generally pleased with them. The neoprene neck gasket does allow some leakage if you spend time being active in the water, but it is minimal, in the order of spoonfuls rather than cupfuls. Breathability is fine for our purposes - can't comment re comparison with Goretex, since I've never used a Goretex suit.

I did have the neo neck seal on mine replaced under warranty by Kokatat after the first full season of use - several large flakes of rubber had peeled off the gasket. Mine has also developed leaks in the right bootie - a dive tech friend says it's almost certain that the stitching is the source, and that aquasealing the seam will cure it. Since I wear merino wool socks that stay warm when wet and usually wear waterproof boots, it's not a huge issue...My wife's suit has had no problems to date, despite equal usage and handling...

Finally, be aware that the warranty is two years only - the Goretex suits carry a lifetime warranty on the fabric itself. If I planned to use a suit often and hard, that would justify the cost of Goretex. Since we really do the bulk of our paddling in about three months of the year, and don't give our gear hard use, the SuperNova is a good compromise in features and cost for our purposes. It is certainly a major, major improvement in thermal protection and comfort, both in the boat and in the water, compared to the 3mm Farmer Johns we previously used...