Good classes (as of 0.8 BETA 2):
Scout (very good Sidearms)
Marine (nice shotting time when using Combat Shotgun or Pulse Rifle)
(My) early game strategy:
Pump Sidearms - explore the first level of Civilian Tower and gather ammo and exp.
Proceed to Security / Military (or Main) Tower. Search for Combat Shotgun there.
After getting it obtain the Colt and ammo for it from Storage Tower.
Ascend through Security / Military and look for Pulse Rifle.
Pump Light weapons.
After Sidearms and Light Weapons are at advanced or expert level, pump other skills.
Mid game:
Ascend through Security / Military. Look for Gyro-stabilizer and Smartgun. Pump Heavy Weapons.
Late game:
Ascend to the top of Main Tower (excursion to the top of Military can be beneficial, btw), kill the Queen, run as fast as possible out of there.
By that time a player should know where the lifts are placed (screenshots work wonders) and should follow the shortest way to the Civilian Tower, level 1.
Some tips:
- Use Space + direction to open / close doors; Try opening the doors from the different angles - there may be several aliens in the room, but only those who are in your sight will go after you;
- The strongest weapon should be ready all the time; switching to Light / Sidearms from Heavy is faster than doing it the other way;
- Try to keep Smartgun ammo for Elites; the rest can be killed by almost everything;
- I use to leave ammo and medpacks near lifts, so on my way back to level 1 I don't run out of it.
Radiation can be very annoying, but there is always Storage / Medical Tower where you can recover the lost HP.
Rad suits are good if you can live with a Pulse Rifle (and Sidearm weapon) only - without the Heavies.