Is there any way to slow the game down? I don't remember it being so hard, and I think its because the speed of the game is super fast...

Can't offer a solution. But I agree. The game does run too fast. GOG should allow away to slow the game down through dosbox.

I don't really have any experience with GOG's Blood but I do have experience with dosbox. Try pressing Ctrl+F11. This slows down DOSBox.
[Note*]You can just hold Ctrl while hitting F11.

The game was always really, really hard.

The game doesn't run fast. You just need to get used to the gameplay.

Open up dosboxBlood.conf or dosboxBlood_addon.conf (for Cryptic Passage) in your Blood directory. Scroll down to the section that looks like this:
core=auto
cycles=max
cycleup=500
cycledown=20
By default, DOSBox is running as many CPU cycles as possible. Changing it from "max" to "auto" will only cause DOSBox to switch to max when appropriate. If you really need to slow it down, try setting cycles to 80000 and test and adjust as you please.
Check out this wiki for more info.
Hope that helps.

You actually need to increase the cycles over the top if you want the game to slow down. I don't know why it works like this, but it does. Creates a sort of a bullet time effect.
I still don't see why would anyone want to do something like this. The game is most enjoyable at normal speed and is meant to be played this way.

I myself find no problem with the current speed. Blood has always been difficult as hell.

If you're saying it's too fast, I think you're playing the wrong game for you then.

In all my time tweaking the game, trying out different methods to play it and new things in general, I have never ever experienced the game running faster than usual, or have ever heard anyone ever report a case where the game runs too fast.
I've seen the game run too slowly, I've seen the game run so that only physics are slowed down or distorted (being able to jump quite a few meters high in laggy multiplayer), but nothing like this. I seriously don't believe that this is even possible due to the nature of how the game is made.
OP is referencing that he doesn't remember the game being "so hard" and "thinks" that it's due to speed.
Of course I'm not going to believe that the game is actually running too fast because he thinks it is too hard.

I have a Duo Core 3GZH, with 4 gigs of memory and the game runs fine.
You really need to tell us more details.
Blood has always been notorious as a hard game. I reccomend the even if you are a FPS junkie who usually plays FPS Games at Normal or higher levels of difficulty, that first time through you stick to the lower difficulty levels for Blood. THier lowest "Still Kicking" is probably higher in difficulty then "Normal" in most games.

Disregard other replies, when I owned this game on CD with Windows 98 the game did not run this fast. You can still play it running that fast, try no running through the game, it slows it a bit.

I'm really don't understand this topic. In my terms it run as it always to keep the asses blank.

Just look at Youtube gameplay videos and compare the speed.