So, out of curiosity, I took on a hotel review assignment, and I'd definitely say it was a good experience.
There were some glitches (missing instructions, ahem), and it was a lot more work than one might expect, but the bottom line (and the real test) is that I would do it again.
You pay attention to everything: that tiny dust bunny lurking behind the potted plant, the imperceptible crack on the ceiling, whether a staff member made eye contact with you and smiled or not. And you take copious notes about it all.
You feel like a spy, and in a sense, you are one (for the hotel company). (Of course, as spies, this photo is not of our hotel room. We wouldn't be very good spies if we posted photos of our hotel room on our blog, would we?)
The purpose isn't to get the slow doorman in trouble or point out that the housekeeping staff was picking their nose in public. It's so that all of the new people hired can learn from what their peers are doing correctly (or not so well). If someone is especially rude or lazy, they suffer the consequences of their actions, but on the positive side, I also get to point out who did a great job. And I met some really nice staff at the hotel, so I hope they get rewarded for their good work.
The worst part of the job was having to be difficult and recording how people responded to my complaints. The best part of the job was ordering the room service and rating the food, which was very good. I think I'll look for more food critic assignments next.