First mod or not, my rating won't be any more or less harsh.
As your first mod, it's a fairly average compared to most others firsts. Your texturing could do some work, as the colours are quite plain.
Also the icon does not seem to be working.
He's a bit overpowered compared to the rest of the heroes, I think it's more fair and fun when it's more balanced. 3000 hp is quite a lot and plus with it's 50 hack dmg and 1 population cost make it seem like an optimum, cheap powerful unit for other players should it be trainable.
However, the pestilence effect you have on him is interesting and as far as I've seen the first time it was used on a unit here, so you get some points for that.
Lastly, if you can improve your texturing skills and perhaps even move on to modelling, your submitted mods will definitely get higher ratings than this, and I hope you can come to that. Your ideas are great, your effort just needs a bigger push.
My first mods are similar in quality so there's nothing to feel bad about it