The biggest advice for Ensenada is not to take the Bufadora or horseback excursions offered by the cruise line. You can book the same ones on-site for much cheaper - get a shuttle to downtown ($3 for a return ticket for adults), and they'll drop you off at a ticket counter where you can get the excursion for half of what Carnival wants (plus - they're much more lenient about not paying for kids). We paid $15 for a trip to the blowhole for each person 5 and up - Carnival wants $28 (for kids 4 and up). Also important - be sure to bring cash to Mexico.
Blowhole Walking Tour Rating:
We chose the blowhole because it seemed like the least crappy activity offered - keep in mind that Ensenada is not a particularly exciting location, its prime interest for cruise lines is its proximity to the ports in Southern California, so I lowered my expectations to a minimum. With that, it was surprisingly good - we hit the blowhole at a very good tide, so the water shot up in the air very high; it was off-season, so it was not packed, and the peddlers were most certainly not aggressive, even though virtually every review claimed that. I guess people are a bit sheltered. To get to the blowhole, you have to walk through a large flea market, and every thirty seconds, someone will try to sell you something, like pharmaceuticals and knock-off watches and handbags (one of them offered to "rip you off for less!"). But they're not in your face, and if you say "no thanks" once, they'll get you go.