You'll first notice the lack of the mult level icon bar from the top of the UV editor, and that the tools have all migrated into the new UV ToolKit.
I think the best bet is going to be to take the tools you like,and put them on the new UV editor shelf .. unless you are a fan of the toolKit style of controls.
I'm digging the new Color By Shell option to show the different shells, and while I still prefer to select my edges, and then cut UVs, having the cut UV tool work interactively in 3D space is a very nice addition.
Senior Techincal Specialist Steven Roselle takes us through some of the new UV tools and UV ToolKit in this video
full list of update 3 improvements