Completed the demo on hard on my first run, but had immense fun doing so! The dice mechanics are solid and there is a lot to think about.
The one thing I disliked a little bit was the mana and spell system, which often overshadowed the dice abilities. It's good, but I feel spells should cost more to offset the flexibility. This is less of a problem once you level up a bit and the dice start getting better compared to the spells.
Other than that, really solid. I loved the variety of mechanics between the various monsters, had great fun upgrading my guys to completely new dice and can't wait for more.
I would definitely pay more than $3 for the full version - don't be afraid to ask for money for this one!