I tried out Hammer 5 / Source 2 Hammer yesterday. I absolutely love it.
I did something really quick just to see how brushwork is done in there and I'm pretty satisfied with the tools. (forgive that the architecture doesn't make sense in the following screenshot) Since it was my first time, it definitely took me about half an hour to get this done.
But I guess that's still fast because if you tried to do that many smooth corners in good old VHE 3.x, it'd take you a bit longer than half an hour, lol.
I did almost everything in the 3D viewport, I used the bevel feature a lot, as well as extruding faces and edges where I needed that. It basically feels like I'm using a Hammer'ed version of Blender, really. It's brilliant.
If Valve provides a Source 2 SDK (and they most likely will in several months), with source code so we can build mod/game DLLs, then I'm probably gonna ditch Unreal Engine 4 and idTech 4.