Ha. Hey Andrew! It's Callum.  Small world.  
I would really recommend looking into some live performers.  
And I realise that some are harder to acquire than others, but at least your guitars could use some live treatment.  
I like how you said that you played all of the parts by hand.  
That means that there's already gonna be some humanistic (is that even a word lel?) feel to it in terms of rhythm.  
That snare kills the drum part, have you compressed the drums at all?  
Plus, the hi-hat feels like it needs some more variation and velocity quantization.  
The part from 0:40~ onwards until 1:00~ sounds REALLY good in the drums (minus the snare).  
Your kick sounds like it has no substance, try boosting some low mid frequencies by a few db and perhaps 10kHz by a few as well. You'll get some solid thumpage from that.  
I love your own additions to the arrangement here. Mind you, I've loved all of your compositions, so I don't doubt that.  
It does feel like it needs a better, more thorough ending though, just to fit with the genre. Maybe a double time section?  
Also, that brass sounds so hella good. I think you're better off calling this a Power Metal mix than just a plain old metal mix. Haha 
You can notice that the bass is not real unfortunately (and in my favourite section it's most noticable(0:40~ - 1:20~)  
Also, how much Reverb/Delay have you used?  
Don't let this dishearten you though. This is really good. And I know for a fact that you have the skills to get this to an OCR Mix Post standard.  
- Callum