The training you receive is always subject to the instructor you select. Most people do not know what questions to ask until after they have taken the class. The PADI cavern class can be a good class given that you have the correct instructor. HOWEVER and this is a big one. Most of the other agencies NACD, NSS-CDS, IANTD (I'don't know about GUE but I will assume they are the same) do not accept the PADI cavern certification should someone come along and request additional training towards the full cave level. One has a hard enough time going from one instructor to another within the above agencies(NACD, NSS, etc) attempting to move ahead in certification let alone showing up with a PADI Cavern card.
The cavern class is not a glorified AOW class and should not be looked upon as such. It should be perhaps one of the most intense and demanding training levels of the cavern to cave certifications. Divers need to develop their buoyancy and trim, propulsion techniques, reel work, emergency handling techniques and an awareness of the cave environment, and dive planning practises. Each level after this further develops the diver and hones those skills. At cavern and Intro there should be little difference in the skill requirements with intro having even higher expectations. Going onto to Apprentice will include yet more development and the introduction of jumps, gaps, traverses and simple navigation in the cave environment. At full cave you better have your act together otherwise you should not have become certified as a cavern diver.
The NACD is coming out with a new student manual and we believe that the issues of standards, knowledge and skills expected for each level has been addressed. Due out in January 2005. Cavern will be a demanding class.