Being a regular challenge mode player, I really don't mind unlocks based on skins. This is odd since I have other games with skins locked behind surviving X waves, and/or beating levels in under X minutes. Those drive me nuts, so I kind of get it; however, in JWE there is no unlock based on surviving X waves, nor is there an unlock on beating something in under X hours. Challenge mode is almost like the campaign except with less money, better fossil quality, and very slightly increased disasters (if at all... I think it's the same as Pena). Therefore, the unlocks are not that disimular then simply playing a campaign, and unlocking them there. At least, it's about equivalent once the first star is unlocked.