Very little.
Watch a group of drysuit divers assemble for a dive and one thing that hits you is how remarkably similar their drysuits are, despite being from different brands: all have similar zip and pocket locations, panel shapes and seam locations and all use the same 3rd party valves (Apexs or Sitec). The only apparent difference is the branding.
Sporting manufactures need to convince customers that their relatively simple products are somehow vastly different from nearly identical products from competitors, so there's a lot of bumf on how their trilam or neoprene is somehow unique, despite coming from the same Chinese factory as the others. I doubt many people could notice the purported difference once in the water.
A review here will bring up posts on suits that started leaking faster than expected, and surprisingly these are often the more expensive suits. In some cases that's a manufacturing defect, such as poor seam sealing. Sometimes it could be just wear and tear: all drysuits become wetsuits eventually.
What is important is fit (do try to get a custom fit) and ability to add accessories such as dry glove rings, user-replaceable neck seals, offensive color choices, etc.
It would be interesting to remove the logos from a $1500 suit and a $3000 suit, and ask divers if they can tell which is more expensive, and why.
I have a $3000 suit, but my next one will be a $1500 one, as I don't see any significant difference.
Cheers,
Rohan.