Maybe they thought since they look like kids, she should be flat-chested. Or...because of Rika. Either way, Lambda isn't as flat-chested as Bern. Which makes me curious on how they'll draw Erika (if it's still Deen who'll do the adaptation). Flat-chested loli are EVIL~ XD
About the quality, it's good overall IMO. The graphics are good, the adaptation is so-so, seiyuus are also good. Now if it was KyoAni who did it, we will have Umineko moe.