At the southern tip of Baja, Cabo is beaches, condos, party in a desert that ends where the Pacific meets the Sea of Cortez. This is a tourist town and you can tell as you are constantly solicited for tours, fishing, merchandise, restaurants, etc. Shore excursions tend to be unnecessarily expensive. Oddly enough, despite my "3" rating, I have had a good time both visits. I will focus on just the immediate area.
If you are not into snorkeling, the submarine is a pricey, but very good one hour view of the colorful fish and a topside look the the rocks, sea lions, and such. Otherwise, if you want to see something, take a glass bottom boat out to Lovers Beach. If you are willing, it is not too difficult if you have a group to negotiate to about $7 per person. They will take you out to Los Arcos, the famous rocks, show you the sea lions, see fish in the glass bottom, and they will drop you off at the beach (can't really walk to it), and pick you up again whenever you want. Note that you need to be able to hop out of the boat into the water. The beach is nice and away from the hotels. Walk between the rocks to Divorce Beach also. This makes for a nice several hours. Along with a little shopping, for me, that's about it and I'm ready to go back to the ship.
Since Ensenada itself is not very interesting, a half-day trip to somewhere is a good idea. If you've seen the blow hole (and maybe even if you haven't), take the Winery Tour. Take a bus for about 45 minutes inland and visit two wineries. At one you will get a tour. At both you will do tasting. The wine isn't really that good. But the L.A.Cetto Winery is pretty. I've been on it twice and it just makes for a pleasant few hours. And... it is inexpensive.
There is not much to see in Manzanillo itself. But, it is a great gateway to the interior. I have taken two tours to different towns and ruins. The countryside is green and very nice. And, you will get a good taste of the real Mexico.
I've been to Puerto Vallarta before and about the only thing I like the the malecon. Otherwise, the Tequila Factory Tour was fun, interesting, and a very good value. You make two stops. They are small operations that make 100% Agave Tequila. So, it is not a big factory or anything like that. So, it is pretty up close and personal. There is lots of tasting of quality Tequila. I would definitely recommend it just for that. The "Old Town Tour" part of it was really nothing but at stop at stores and a drop off.