It's not a bad idea but we REALLY need a "skip battle" button, or at least a 16* speed since there's absolutely no point in watching them.
Also, I think you've drastically misunderstood the point of the medals. They're meant to be a challenge for those playing the game, not for those obsessed with it. I'm just up to 500,000+ gold and I've noticed the mark is 5 mil. That's ridiculous... There's not even anything to spend it on!
...Though maybe it would make sense if that "level 45 on endless" medal weren't actually impossible. I understand you made changes to stop people getting an infinite game with Romeo-S, and I'm guessing you made them too far in the other direction. As it is now it should be chest every 10 levels and the medal at 30, because 45? Not happening. With my Juliet-S/3 Shadowkillers/Devourer (gemmed-up as recommended) I can occasionally make it to level 32-33 but still average below 20. Other suggested combinations do a lot worse.
The sound/music is a little annoying, the game levels are unbalanced, it's frustrating that the max gem level is relatively low and that the medal is the only reward for reaching the max (it'd be nice if, say, completing 2 branches game a bonus gem), and the battles... There MUST be a better way to set those out visually. The art style the game has is quite striking but is wasted when all the characters are piled on top of each other. Speaking of creatures, it'd be nice if they seemed at all weighted towards giving me ones I DON'T have from chests. Is there even a limit on how many times a certain one can be obtained? It'd be nice if we could trade spares in somehow or another, maybe a mini-game to up our odds of getting the ones we still need.
So yes, it's not terrible and I'll probably aim for the "all 5 races" medal before stopping, but it should have been a lot better.