Basically, if you have to ask what makes them so special...then you don't really understand the issue. I believe that the SEAL training syllabus is nearly two years in length, learning everything from soup to nuts about special warfare. They do go to other service schools to learn specialty stuff like jumping out of perfectly good aircraft.
Because SEALs are water creatures, they are different from the other SPECOPS dudes in that they spend most of their time training in the ocean. I am NOT denigrating the other guys at all...they are all true warriors and great at what they do. I am simply stating that the SEALs add another dimension to the training of a special warrior. And yes...I am well aware that the other services also get wet...but not like the SEALs.
If you like to swim and can stand the bitter cold of the rough California surf, on top of all of the other stressing training, then maybe SEAL training is for you.
One of my best friends and old shipmates has a SEAL son. The kid is now a LCDR snakeater and one of the calmest, most intelligent officers you would ever want to meet. He is also one of the coolest, baddest dudes on the planet. I would NOT want to be his enemy.