There has certainly been a lot of evolution in genestealer models over the years.
The picture below shows the very original plastic genestealer from Space Hulk days of yore compared to a more "modern" model (well -- from the 2000's at any rate).
I've noted this before on different posts, but ignoring the different plastic technologies, it is readily clear that the newer version is much more dynamic and can be posed in a variety of ways. The sculpts are also subtly different: the new version's exoskeleton appears stronger with fewer weak-spots compared to the older counterpart that has exposed flesh in the centre of the back. This has been replaced with a more boned exoskeleton along the back that looks radically different. Clearly the hive mind has been at work over the years. The new model's rending claws are also better looking to me, but the more human, rear pair of hands are broadly similar. I might go as far as to say that the older genestealer's human-like hands are preferable given their dynamic look; the newer one can appear like it is about to slip on a pair of mitten gloves before venturing out in to the dank, chilly service tunnels of the Space Hulk. Regardless, I still have a few very old genestealers knocking about the collection. I think I might even have a lead patriarch in the mix somewhere as well.
With the new codex about to be released, I might well dust off some of my very old models and see if I can re-purpose a few of them for a genestealer mini-cult.