Pretty good for a first, but one thing I hate is the border. Choose another border..IMO the border doesn't necessarily have to be noticed at the exact time you see the siggy..

Also I'm not so fond of the text on the right; scary monsters shouldnt be in a tech siggy ^^;. Also the text you use for your name on the top left doesn't match with the theme..I suggest going to dafont.com for your needs of texts :-)

I also dont like those black horizontal lines..

The BG needs to be changed, good brushes can be found at deviantart.com.

Under the creature's right arm is some grayish bars..not sure if that's supposed to be there but if I were you I'd use the magic eraser and take it off.

Having said that it's a good first siggy, and you have some potential!