Honestly, I think it sounds good for what it is. It's power metal firmly rooted in the days where quantizing, meticulous editing and wizardy were not as prevalent as today's modern metal and digital recording. To keep the feel, I wouldn't say there is a whole lot you would want to do...The improvements could/should only be made by the musicians and their performance/technique. For a demo, I think it's pretty good.
So, I'm late to most 80's metal...I was too young to get into it then. But, when I listen to Reign in Blood nowadays, I hear the mistakes and production as much as I hear the songs, and that's a bummer...Todays metal production "standards" have spoiled us in their relative perfection. I'm slowly getting to where I can find a comfort zone in listening to a "truer" representation of a band, and this demo is where this band is at the moment, for better or worse (in terms of performance/technique). And, that's fine by me for any band.
But, I'm just a noob when it comes to production and engineering. I'm a hack player, too, so maybe that's why I'm more lenient...