Managed to overcome the first location, I think the secret jem is very restrictive for the introductory location, I didn't notice any hint of it hidding behind the bush, and on the left there was obvious unreachable gem keeping me retrying to get it.
Very soon after the first location I encountered bat battle where bats just kill me constantly and I just can't do anything against them, and I even don't understand what to do next - should I continue to collect jems, or find another path, or kill bats with help of other hero - it's totally unclear. I've retried until game allowed me to press "Continue" but after some number of retrial this option disappeared and only "Restart" was available, and I gave up.
Nice graphics and music, btw! Maybe it's just me not getting the gameplay right.