I find it way too fast on my computer. Played it on my dad's computer, and it was just about perfect - slow enough to dodge bullets. The game just does scale well to the hardware.
Finally caught the hint to use halflings on the final battle. Once I had 9999 mana and all the defensive upgrades, I started summoning Angels. Let them take down the castle. Continue Angels until Ender gets to your arrows' maximum range. Then start shooting while summoning Halflings. Summon another Angel whenever the timer is up. The Halflings don't do much damage, but they slow him down so your arrows do more damage, and you have time to summon more Angels. I finished with 8000 health.
 "Mushroom Revolution"){kind=icon}
 "Mechanical Commando"){kind=icon}
 "Epic war"){kind=icon}