Here are some tips, if you feel the gameplay is still too tough:
Remember to check the Readme file first. There are description of the whole ideas, and some info that may be useful for you.
Get a better weapon. Find a submachine gun, rifle, or shotgun ASAP. You can use them to eliminate enemies more efficiently, and there are lots of them in the maps.
Find more useful items. Bandages and medkits are really helpful for your survival.
Loot things from enemies. When human enemies die, they'll possibly drop extra useful items, aside from their weapons.
Aim to the head as much as possible. Even hitting helmet is better than hitting body.
Take advantage of the surroundings. You can make full use of advantageous places or obstacles, to reduce the chance of being hit by enemies.
Use telekinesis shield wisely. Remember this can block bullets. You'll be quite safe as long as it's on.
Use hand grenades and RC bombs when situation is suitable.
Practice more. After all, taking some time to practice is necessary. It's a better way to improve your skill, get quicker reflex, etc.
