there are 2 new stargate mods that just came out for Halflife 2. "Stargate TC2" and "Stargate Legacy".
TC2 was/is AMAZING! totally worth checking out! Weapons aim is very cannon and very easy to use! Also it lets you add your own maps! The gates as well are the best out there besides Avons gmod10. Everything you shoot in the gate comes out the other end! The only downside is the gates lead to a dead end due to game modes.
SGL is bad. GREAT ideas for weapons and maps....but horrible aim. you have to guess and even just randomly shoot. no Crosshairs EVEN! They have "iron sight" but even that is a guess and miss! Also they don't let you add your own maps.
So in my opinion TC2 is the best you can get....and let me tell you our mod for hl2 will make tc2 seem like child's play. And Tc2 is AWESOME!