I've been using Hammer since the Worldcraft 3 days, it took less than an hour
of using TrenchBroom to know I'll never go back to Hammer or JACK.
It just works. The overall modelling workflow is much more efficient, it's well
designed, linked groups is a killer feature, it doesn't crash for no reason and
when it does crash you can submit an issue and get it fixed in a day (or fix it
yourself, it's FOSS), CSG (e.g. the carve tool) produces sane geometry in a few
milliseconds instead of crashing after a 20s freeze.
It also runs smooth and fast whereas hammer stutters all the time and feels
like it renders its viewports and UI at 20 fps.
The apparent simplicity is a feature in itself, not a lack of functionality.
It just works. The overall modelling workflow is much more efficient, it's well designed, linked groups is a killer feature, it doesn't crash for no reason and when it does crash you can submit an issue and get it fixed in a day (or fix it yourself, it's FOSS), CSG (e.g. the carve tool) produces sane geometry in a few milliseconds instead of crashing after a 20s freeze.
It also runs smooth and fast whereas hammer stutters all the time and feels like it renders its viewports and UI at 20 fps.
The apparent simplicity is a feature in itself, not a lack of functionality.