For me it is 1. Terrible quality of all rubbery/soft elements. 2. If it is original model (instead of ripping of existing set), it often contains huge, shell li

For me it is 1. Terrible quality of all rubbery/soft elements. 2. If it is original model (instead of ripping of existing set), it often contains huge, shell like elements, that can't be easily be in custom designs. 3. I guess the previous point doesn't really matter, when bricks are designed to be assembled once and are impossible to pull apart without hurting your fingers.