I love the same thing that I hated which was that after 20 minutes, I was still clicking away.
Most such games "fill up" and when things pile up the game gets hectic until one can no longer manage.
Your game is different. The further one plays, the slower it gets and the more thinking is needed until the ultimate idea pops up which is to start another round.
Really great concept.
You think different (and different is good).