Since Heartseeker has been out for a while now, I thought I'd share some optional tweaks to the rules.
Clerics get prayers equal to half level rounded up. This means you'll at least get one prayer per day.
Wizards get spells equal to half level +2. Just gives them a slight edge, but not enough to turn them into some magical lunatic.
Lower ACs for some creatures. I'm thinking goblin here, whose AC could be lowered to 11 or 12. Since high Physical only offers you +1 to attack and damage, lowering some enemy ACs for low levels can be a fairer trade off.
Different damage for weapons. This would simply be giving a -1 to light weapons and a +1 to heavy weapons in terms of damage.
Every game needs a soundtrack. Ok, no EVERY game (noughts and crosses, for example), but roleplaying games do. Here's Heartseeker's:
Whitesnake – Here I go Again
Ratt – Givin' Yourself Away
Queensryche – Eyes of a Stranger
AC/DC – Thunderstruck
Dokken – Dream Warriors
Dio – The Last in Line
Bon Jovi – Runaway
Scorpions – Winds of Change
Guns n Roses – Rocket Queen
Rainbow – Tarot Woman
Poison – Nothin' But a Good Time
Savatage – Hall of the Mountain King
Iron Maiden – Wasted Years
Because Heartseeker is only two pages long there's no real art in there, but when I was writing it I had visuals in mind for the type of stories the game depicts. The feel of Heartseeker is super 80s – painted, realistic fantasy.