I have seen some forum threads regarding HL1 vs. HL2, and many people complaining about hl2 mapping and why they prefer to map for Hl1.
I'm going to make a list of some good and bad things regarding mapping for both games. People can add to the list and maybe some popular doubts about source mapping will be cleared.
What's good about Source mapping
-High resolution textures
-Selecting a reference brush when making a new one (automatically allows you make a brush just as tall/wide as the selected one)
-Detail brushes that give shadows but dont complicate leafthreading
-Shader effects (cubemaps, real-time reflections)
-Huge collection of props and decals/overlays to dress up the map
-Advanced trigger system (very advanced in fact)
-Sound library built into Hammer for easier access.
What's not so good about source mapping
-You need to logon to Steam, and load Source SDK...
-Occassional random hammer crashes
-General system slowdown (high memory usage)
-The amount of detail possible makes mapping much more time-consuming, sometimes forcing you to place props and more props...
-Default textures and props always end up in maps looking very similar, very "HLl2ish"
-Absence of an intuitive SDK program for creating materials
-Default skies seem to dictate how the light_enviroment has to be, making other light angles and colors look weird.
What's good about HL1 mapping
-Hammer 3.4 loads fast
-Textures, although not high res, can be placed next to each other and usually look right.
-Since detail is not the most important thing, making a nice and fun map is not a matter of years...
-At the same time, making a detailed hl1 map is much more of a feat than doing so with Source
-WAD files. Wally. A huge freedom for creating custom textures.
What's bad about HL1 mapping
-Less Hammer features
-Absence of displacements makes irregular terrain a much harder thing to do, either with VM of using Gensurf
-In SP mapping, it takes a lot of work to prevent a map from feeling empty (not so important in HLDM)
-No entity hierarchy (think about a brush rotating around its center as it's part of another rotating brush)
-Very poor and cryptic trigger system. (Hard to find mistakes)
Okay, I'm sure I left out many other things, so feel free to contribute to this thread