I am actually one who enjoys the secret lots, in part for their mysterious lonely atmospheres and in part because they remind me of fun secret lots in earlier versions of the game (I especially liked those hobby lots in TS2). I agree with everyone else that they could have been better implemented, though, with at least one aspiration (perhaps under the Nature category) that involved finding and exploring secret lots. and maybe some unique collectibles or a profusion of collectibles only available there, or an exclusive activity (with powerful moodlets and boosts) to be found there. It would make gameplay surrounding them much more purposeful and fun.
In Island Living, I don't necessarily mind that there is not a dive lot for all sims, but I would absolutely have loved a secret, magical-looking mermaid lot underwater (even with a loading screen), where mermaids could hang out together, find unique collectibles, fill all their needs and see unique aquatic life. It would have been a wonderful motivator to play with mermaids, and, if mermaids could bring along their friends once they had achieved high enough fitness skill and friend levels, it would even have made befriending them feel more worthwhile and necessary. In general, TS4 would benefit from more purposeful and inherently motivating gameplay.
