I like the grass (can be irritating if they're hiding in it) but you can remove the snow, rain, particle effects (smoke on tank) with a script
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//Atmospheric effects, particle and gun script
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//By pressing this key (F6) you can enable/disable the "atmospheric effects" like rain or snow.
set opady0 "echo ^6RAIN/SNOW ^7 is now ^1OFF; set cg_atmosphericeffects 0; set opady vstr opady1"
set opady1 "echo ^6RAIN/SNOW ^7 is now ^2ON; set cg_atmosphericeffects 1; set opady vstr opady0"
set opady "vstr opady0"
bind "F6" "vstr opady"
//By pressing this key (F7) you can enable/disable the "Particle" system in ET.
set dym0 "echo ^6SMOKE ^7is now ^1OFF; set cg_wolfparticles 0; set dym vstr dym1"
set dym1 "echo ^6SMOKE ^7is now ^2ON; cg_wolfparticles 1; set dym vstr dym0"
set dym "vstr dym0"
bind "F7" "vstr dym"
//By pressing this key (F8) you can enable/disable your gun in your HUD.
set gun0 "echo ^6GUN ^7 is now ^1OFF; set cg_drawgun 0; set gun vstr gun1"
set gun1 "echo ^6GUN ^7 is now ^2ON; set cg_drawgun 1; set gun vstr gun0"
set gun "vstr gun0"
bind "F8" "vstr gun"