Cruises from San Diego to Mexico are generally divided into two types. There are 7-day or longer cruises to the Mexican Riviera, or there are shorter cruises to the close Baja ports.
Disney Cruise Line has some cruises from San Diego to Mexico. CruiseLine.com has lots of reviews of cruises on the Disney Wonder. They are by verified passengers and most rate the ship very highly.
Holland America Line has a lot of experience with cruises to Mexico from this port. Take a look at more than 300 reviews of Holland America cruises to Mexico from San Diego on Cruise Critic. "Excellent" is the most frequent rating.
Norwegian Cruise Line offers long 11-day cruises to Mexico from San Diego. Browse the CruiseCritic reviews of Norwegian Cruises to the Mexican Riviera. They get a whole range of ratings.
"A Mom's Take" offers this video review of a Disney cruise to Mexico. It's about the whole experience.