Is there some mod that simplify them or something? I began playing this game to become a thief but I find myself trying to kill or sneak past zombies or beast like creatures and I don't find it interesting at all, just a huge time waster. I'm also playing on Expert because I wanted to actually explore the game and find everything but it's rather boring knowing gems and what not will be guarded by some creature and I don't find sneaking all that much fun against creatures.

I'm currently on the 4th mission and I'm out of potions and just stumbled upon a burrick nest, four of them and non-holy water arrows in this game blows, enemies never die which I believe they made it so to push people away from combat which is completely understandable but then they design the game to have enemies you kind of need to fight and that's what pisses me off.

You can blackjack burrick or kill it with your sword (a bit time consuming though).

Yes and it's hard if you meet more than two in a small room. I managed to run through the nest I found so that's ok but I'm back meeting these annoying zombies and top of it, a fire shadow that can't die.

It's been a while since I played the game, but if I recall correctly you can continuously hack zombies until they temporarily die (they won't die permanently, but they will sort of faint and as long as you don't get near them they will not resurrect again).

What's a fire shadow? Do you mean those fire elementals? You need water arrows for those, which of course can be hard if you run out of those.

I went to the wikia and apparently there's only two fire shadows in the game, once in 4th mission and once later on.

They are like zombies but faster and when you have hit them enough they flee instad of fall down and die temporarily but they come back in case I leave the place where it is standing guard.

The problem is I can't hit it that securely, I die by one hit currently due to my low health and backstabbing it is not an option because even if they walk they're faster than my walk and if I go forward without walking (running?) than it hears me, turns around and wack me.

It's possible they are only part of the Thief Gold version and not in Dark Project so if you played the latter you never met them.

I just checked the Thief Wikia.
http://thief.wikia.com/wiki/Fire_Shadow

Now I remember :-)
I think back then I just tried my best to avoid them, or hit them until they flee and finished whatever it was I needed to do before they came back. Sorry I can't be more helpful in this case.

I can't avoid it because it blocks a puzzle of sort I think and I might need to for gold or supplies. I think there is one or two zombies alive where the fire shadow is and I tried to lure out the zombies to wack them one at a time leaving them temporarily dead at each place as I can't afford to waste water arrows by using a holy water then shooting 2 or 3 on each of them, when they're temporarily dead only 1 holy water arrow is needed so then I could finish them off, if not just run away from that place when I've finished the puzzle.

Are you in the Bonehoard?

You do realize you can use the fire traps to destroy the zombies?

I was but no, I didn't know that. Luring them there would have taken it as much as time as destroying them one by one though.

But it's loads of fun!

True, I would have definitely opted for that if I had known it. I know so hopefully I'll be able to pull something similar later on.

Later on, word of advice, buy plenty of holy waters and flashbombs. And bunch zombies together (for the flash bombs).

You can sneak past zombies too. Also, flashbombs will kill them, which is cool because you won't be using them to blind guards in the Bonehoard. Use them for zombie-killing instead. It does take several flashbombs to do it though.

EDIT: I should perhaps re-emphasize that sneaking past zombies is the easiest way to deal with them. They are slow and pretty dumb, and it's actually easier to sneak past them than it is to sneak past guards. If they see you, just run away, they're too slow to catch you and they'll give up looking quickly. When I first played I thought the zombies would see me no matter what so I always tried to fight them. Later I learned that I can basically ignore them in most cases.

Burricks are easy to kill - just line yourself to their backs and swing away. Always stay behind them as they are extremely slow turning around. This goes with any other close combat mobs.

What I do first is perform that massive swing (hold down the left mouse) and run behind them and then let go of the left mouse button - then slash a couple of times after that and they eventually run away. Then it's a matter of chasing them down for the final kill (or broad arrow them if you want).

Zombies, just jump past them as it's faster than running. I had heaps of zombies 'chasing' me only to give up a sec later because of that speed jumping. Make as much noise as you can as they are just idiots. And don't think about locking them up in a room as those bast@rds open doors.