Natural Selection/Alien strategies

Skulk Rush!
In 1.04, it was pretty much a requirement that the entire Alien team rushed the Marine base at the start of the map. It usually didn't kill them, but it slowed them down a lot. If you can get a lot of people to rush at the same time in 2.0, it can really surprise them. Still, since Marines get some res per kill, make sure its worth it.

Gorge Rush!
Surprisingly, a very effective strategy! Heal spray heals friendlies as well as being an attack to your enemies... so what happens when you have a huge group of Gorges all heal spraying each other, running right towards your base? Well, the group is going to be near impossible to kill with just LMGs. After you've killed all the Marines, have 1 or 2 people go Skulk to kill the IPs. Extremely effective when done well.

Res Rush!
The "standard" strategy in public games nowadays, because its easy and super effective. Too effective in my opinion. Everyone runs to a node. Goes Gorge. Drops a res tower. Go back to Skulk. It almost an instant, your team has captured every available node on the map.

Stealthy... like the Ninja
REAL ULTIMATE POWER!! Well, not really. If a Sensory Chamber is dropped first, its going to greatly influence how you play the game. Oddly enough, its the most defensive of all the chambers. Use Cloaking and Scent of Fear to hide outside their base and prevent them from expanding. Drop the chambers inside your hive and in other critical areas, so Skulks can get right in the enemies face before decloaking. It's really not a good idea to attack head on during this time, as you'll most likely just give the Marines more resources.

You have Movement, so MOVE
I love movement chambers so much at the first Hive. Their upgrades make Skulks very, very deadly. You wouldn't believe it at first, but silence really makes you a more effective killer, especially if you attack from behind. You could kill an entire squad of Marines without them even knowing! Celerity is a great upgrade for the Skulk as well. Theyre already hard enough to hit, theyre REALLY hard to hit when their speed has been upped. Celerity is also great for Gorges to run away from danger, and to get around the map faster. Celerity Skulks should go on the offensive, while Silenced ones lie in waiting. Once your team has Lerks and Fades, they'll have access to Adrenaline right off the bat, making them much more effective. If you go with the "standard" Sensory, Defence, Movement combination, you'll most likely be hurting in the later game, since Sensory loses its effectiveness once the Marines get an Observatory.

Defense that isn't so defensive
The Defense chamber is actually probably the most offensive based chamber. Regeneration can let a Skulk with patience eat an electric resource tower. Carapaced Skulks last significantly longer than normal, and your speed isn't reduced all that much. Redemption is pretty much useless until later game. No matter what chamber your team decides to go with for their first, they are all viable. There is no magical order, save the next strategy. Just use the ones that you have to your advantage.

Defense. 2nd Hive. Always.
If you didn't drop a Defense Chamber for your first Hive, you must, and I stress this very much, drop one for your second Hive. You need some Oni to break the Marine stongholds, and Oni are pretty much useless unless they have Defensive upgrades to back them up.

Gorge - not just for building anymore
Once you get the 2nd Hive up, Gorges have access to the very potent Bile Bomb. This is bar none, the most effective way to get rid of turret farms. If you followed the best, in my opinion, chamber order, you should have Adrenaline and Regeneration. Duck in so only 1 turret sees you, Bile Bomb it, back off, heal, and repeat. Each Bile Bomb does 200 damage to structures, which is basically shooting Xenociding Skulks. Yeah. It hurts a LOT. If they have a Phase Gate however, you'll likely find resistance. Have a Fade or a few Skulks as escort. Bile Bomb is also ideal for taking out those pesky electrified Resource Towers your Skulks were getting zapped by.

The other turret killer
You need a but more patience for this one, but it works. Spiking with the Lerk. Try to get just 1 turret to shoot at you, and spike it to death. Move out a bit more so again, only 1 shoots at you, and spike it to death. Rinse and repeat, and call in the heavy hitters to finish off the Turret Factory using the blind spot you made. Turrets also have a range, so if you can range them, thats even better.

The game has been going on for 3 hours because you're stupid
Some people have experienced games where the Marines have just turret farmed so much, its impossible to clear them out. First of all, your entire team using Redemption Onii just won't cut it. Redemption saves your life, but at a severe cost to your effectiveness. You often Redeem with a good portion of your life left. Then you have to heal up, and run allll the way back.

Regeneration runs on percentages, so it will make you near godlike unless your really being pounded. A Gorge following you with Adrenaline using Heal Spray certainly wont hurt. A Lerk spraying UMBRA, NOT SPORES, is pretty much essential. The rest of the team should be doing the real damage with Bile Bomb, Bite, Gore, whatever you have. Its not that the Marines are hard to kill, its just that you have to use teamwork to do it.