I remember Dolphin being a particularly painful one, and as I recall it ended up with some weird compromises (wasn't erasure supposed to avoid needing to update the bytecode format, but then annotations required it anyway? Something along those lines)
yeah - they took forever, one reason being that Sun was in financial troubles and then acquisition took a long time.
Second was about licensing and Apache Harmony.
So, eventually they dropped most of the big things that were planned - Project Lambda with closures, Project Jigsaw with modularisation, Collection Literals. They eventually came back, but took a while to implement, so it was a prudent decision to make.