You're good at this, a lot better than most that i read... but I am the person who gives critiques to every piece of writing... or atleast almost every piece of writing, on this forum... so here's my critique (and remember, you're a better than most I read, and you're better some people I know who are doing a creative writing degree right now, but there are issues that you can totally fix.)
the massive man's entire body tensing as he saw the creature that came lumbering from the treeline. In an instant, his massive sword
massive man as a term sounds a bit too silly, due to the alliteration, also, you shouldn't use the same word in two consecutive sentences. Massive is used twice here. massive man with his massive sword.
his massive sword was in his hands the chipped and battle-worn blade
punctuation between 'hands' and 'the'
The creature halted, giving the human a good look at it's insect-like body.
why did it halt?
The creature was one not native to his world, that was for certain. It stood on six spindly legs, each one curling to a sharpened point, all of which were currently embedded in the earth to support the bug's weight. It's body was like that of a beetle standing upright, a mix of mottled brown and black chitin covering it's entirely. Where the plates of that natural armor ended, wicked spines sprouted from it's body. Two limbs were poised in front of the creature, each tipped with three long, blade-like fingers. Four beady eyes stared back at the man, expressionless and black as night. A blunt horn crested the creature's head, which now slowly lowered to aim at the man who stood in its way. The plates on the creatures back opened up with a high-pitched buzzing.
That's a lot of description. Probably too much, especially with the rather list-like way of talking about the the different features and how many of that feature there are. Six spindly legs, two limbs poised, three long fingers, four beady eyes. Just pull it back, and just mention two or three things about it. You want to be focusing on what you want the reader to feel when reading about this creature, not what it precisely looks like. Also, "black as night" is a big cliché
Rebel did not pause to think, merely acting on instinct as he dove to the side.
maybe a tad too many words for such an active and quick action... Merely is certainly one to cut.
The insect went flying past, propelled by wings that were previously hidden under it's armored back.
no need to tell people where the wings came from. they can already expect it from the high pitched buzzing of the previous paragraph.
The insect was in the process of turning around
in the process of turning around? doesn't sound exciting.
The insect was in the process of turning around when Rebel landed his first blow
also I'm assuming this is talking about the blow that is going to be explained in the next few sentences? The reader should be riding right alongside the action, not being told abuot it after the fact.
He jumped forward, swinging that massive weapon of his as if it were a base-ball bat, letting momentum add force to the blow
unless there's some modern twist here, is there a need for the baseball bat analogy? also, the momentum thing does not need to be said.
The blade collided with the beast's back with such tremendous force that the weapon was jarred clear out of the human's hands, the blade quivering as it fell to the ground. It was as if he had struck a wall of metal.
again, not much speed in terms of the feel of the battle. I mean, you could easily say that in a much shorter way. Like this:
The blade clashed against the armoured beast, shuddering from the impact, falling from Rebel's hands. The beast wasn't even scratched.
those deadly claws
those is quite a soft and friendly word. and we already know that they're deadly.
as the bug completed its turn
absolutely no need for this
The thing
after calling it the creature and the insect so many times... the thing seems kinda off.
emitted a clicking hiss at him
you could just say
The beast clicked and hissed
it's six legs carrying it forward with surprising speed, arms slashing in a wild attempt to kill its fleshy opponent.
There's something wrong with this... either it's the "surprising speed" when other better words are available, like vicious or "it tore up the earth, charging towards him." Maybe it's the "wild attempt." there's something abotu the word "attempt" that makes it seem so ineffectual. Though probably the one that sticks out the most is "fleshy opponent." This lowers the hero onto the same level as the monster. A faceless entity.
The human
What's with all this "the human, the human, the human," stuff. he's your main character, keep hold of his personality.
There are some other issues at this point but I would just be repeating myself
Rebel growled in annoyance
annoyance? really? this a fight that he's losing. a fight to the death, and he's a bit miffed?
Blood dripped from the fingers of his injured arm, expression stern as he scowled at the dead creature. "Always hated bugs."
oh well if he's that kind of character, then maybe Conan here does merely get annoyed in such situations.
The human pulled himself to his feet with some great effort
don't just say it took great effort. Show it in the guy's actions and voice.
Your main problems are:
I know this sounds weird for prose, but you use too many words for regular sentences.
There's very little sense of fast paced momentum.
You have a very visual sensibility, but that doesnt translate through your prose at the moment.
But the good things are that your visual sense is very strong. You know what looks good, you just gotta make it sound right. Give the feeling of intense action and horrifying sights, not just the explanation of them.
But yeah, this is pretty good.