Great shooting games but the level require to many gem to upgrade and gen cause too much money. Even buy the 24k gem also cant even upgrade the aircraft to max level. U need buy at least 4 set of 24k gem to upgrard to max level, this have not inclue gold purchase. One max aircraft will cause SGD maybe $1000 which not everyone can affort it. It will be good either the price of the gem/GOLD can be lower and most of the game player can affort it