I consider myself a Gem "main" for whatever that means. So let's get some discussion on him.
I'll put in my full thoughts on Gem later, but for now the major differences between older versions.
The main differences between v03 Gem and v04 Gem are that
-Light Ancient Power comes out a bit slower. It used to be possible to trap someone infinitely at the wall with just light ancient power...
-Giga Drain is nerfed. I'm not sure of the original damage it was does, but now Giga Drain does paltry damage compared to other supers, and Gem only gets half the damage back as health, opposed to all.
-Paleo Wave travels slower than before.
-Empty Paleo cancel is now a back dash. And empty paleo cancel is when you execute a Paleo Wave to Giga Drain combo without a full meter. In previous versions, it would leave you in a nuetral state where you are, free to Ancient power/whatever. In v04, you dash backwards, so while you're still safe, you don't have the same follow up potential.
-Paleo Bounce back let's you levitate. In addition to the empty cancel being different, Gem can now levitate on the bounce back lag of Paleo Wave if he chooses not to cancel. This can lead to more attacks, or a Power Gem.
That's all, though I probably forgot something. There are some smaller changes like Power Gem travelling faster and maybe some damage tweaks, someone can point them out if they'd like. Hopefully, I didn't miss too much.
So boys and girls, Gem is likely a top tier character in my eyes, tell me what you think.