*Usually* if it has really awesome gore/sfx, I can look past the acting and plot and everything else.

In my opinion, It needs good dialog, gore, and good acting.

Tie between Writing/Dialogue and Acting.

I think if it's more of a combination of good writing and acting which makes up good characterizations. I won't care whether someone gets hacked to pieces if they don't seem to be like a real person.

PLOT! There has to be a plot. No plot = no sense = not worth viewing.
I don't care how wacko you make the character or how far-fetched the story seems but,dude, got have that plot as a foundation.

Realism would be the second to that.

Oopsie, I've just rambled on^ because I actually did NOT see the part that said "aside from plot ..."
Sorry, I think I need new specs.

In my opinion most importantly, they have to make us feel afraid. send this fear.

I like when writing makes me think... What they have to say can sometimes make more of a impression then alot of other things.

The acting is only bad if the script is written poorly. Sometimes some of the dialogue makes me lol ... ex: the Friday the 13th remake.

But if the acting is really bad... I find myself being less scared and more... lmao.

If its bad writing it doesn't matter how well its acted it'll still be bad so I think the writing needs to be great then you can move on to the acting nothing else really matters!

Some movies now focus too much on having gore and being scary and not enough on the writing. I know you need horror in a horror movie but you also need a movie as well. (If that makes sense.)
Acting is also improtant. They need to make it real. Like Myers_fan said they need to make us scared. Ok I'll shut up now.

Acting, realism and of course blood and gore but its common these days for it all to be blood and gore and they forget about the pilot/story!