I really liked this game at the beginning and through the middle, but that excitement went down as the stages became laggier and I was more and more required to grind the last beaten levels to gain more gold to upgrade my guys for the next, or I'd fall short many times.
I probably spent 4h grinding to reach the end, but that's where I gotta draw the line.
I have everything maxed out, had to revisit the 2nd to last stage like 20 times with severe lag in order to upgrade everything and still fail to beat either the last stage nor the 2 last time-attack challenges.
The reason for that is the lag. Even with quality set to low and no other windows open/programs running, the game is still slowed down to 1/2 - 1/3 of the normal speed. That would be fine since it allows for better dodging, crowd management, etc. but the TIMER is still running in real time. That makes my party run and fight in slow motion basically while the timer still mercilessly counts down to zero. Even with maxed runes it's impossible to beat the time trials. Heck, when there's like 1 sec left there are still enemies walking into the screen, so the spawning isn't even finished by then. So even without lvl restrictiions it would be literally impossible to kill all enemies.
As for the boss, the hoard spawning is probably also based on a timer running on real time. They spawn faster than my maxed out party with maxed runes could kill them. I can't focus on the boss either since the enemies would else overrun my team, kill them within a minute and then focus all on me. Which happens anyway eventually as I can't keep up slaying the hoardes as they spawn.
And since 2/3 medals are based on finishing the game and doing all trials, the only possible medal isn't worth playing for 3 and grinding for 4+ hours.
Never base an ingame timer in these kinda games on real time. They can make such games harder or even unplayable for people who experience lag. Many people who play flash- and indygames don't have the pc for the big AAA games, so it's likely that they experience lag far more often. So if your target audience is such gamers, don't punish them with real-time clocks that their hardware can't keep up with.