I used GTK Radiant for 6 years or so and created bunch of maps but only one survived HDD failure. At the same time i  started using Valve Hammer editor, also great editor for Half-Life and CS I created couple maps for Half-Life 1 and later for Counter Strike one hostage rescue map

All maps are  very fun to play and if you need some old school graphic, and level design then check them out.

Quake 3 - RaP1Dm4  -Space Curve-

    Counter Strike - cs_central