First of all I just wanted to express my love for this game. The Reactor can be frustrating but I usually can (with a few attempts) get all of my Marines through. I think it”s vital as to which order you deploy the troops (my deployment has evolved over time) and (within reason) don't linger and keep progressing from right to left. Try not to create a bottleneck by moving some marines around the top and some around the bottom of the railings/shaft. For this reason I like Apones "listen to Gorman" function. Operations is by comparison easy with a full deployment of Marines. It is time consuming. Again, the order of deployment is vital. Keep your Marines grouped tight to fall back to the door. Once here you can fend off the first and second (last) swathe of Alien attacks. You can rack up some points here. The key here is to use your 2 flamethrower guys in conjunction last, both flaming the ground and retreating one square. You can create a bottle neck and make use of your grenade launcher. I found this level frustrating with Aliens dropping in the tunnels. However you can wait out the Alien attacks and use Ripley to safely dispatch all the Aliens just by waiting at the start of the first long tunnel. The Hive I find very frustrating. The more Marines you have the harder it is in a way. Again, avoid bottlenecks. My trick here is to use the lift as a cage. Activate the Queen by launching a lucky grenade and then flame the ground and all 8 of you can let rip on her.I've yet to rescue Burke and Newt and Kill the Queen with all Bonuses activated but I'm close. What I find frustrating is that (if I was playing for points) you're rewarded heavily for carrying out incapacitated troops not for racking up kills. My technique of the "Lift Fire Cage" also sometimes triggers a glitch which the game crashes from (I'm not sure why yet but an Alien will spawn near a shaft, die in acid and then flame-ball) this is frustrating because it takes time and restarts to run "the perfect game" up to this point. Love it though. Many thanks