The Hissing Wastes as a medium-sized location, whose exploration is optional, because you receive no main quests here. Still, I recommend that you travel there, because you can obtain lots of experience in the Wastes (e.g. for defeating the great dragon), receive many side quests and obtain valuable and useful items. The most valuable loot is in the six, quite vast tombs.
The way to unlock this location: On the war map, select the "Stop Venatori Activity in the West" () operation and complete it. This is possible if you have, at least, 20 Power points.
Recommended experience: The Hissing Wastes are the area that is meant for a well-trained party. Even the standard monsters around rifts may be a problem if your party is too weak. Also, you will have to fight challenging fights with Venatori cultists and hostile creatures on the surface and in the tombs. You should be able to win the majority of the fights, with a party at level 17-19. The only exception is the great dragon that you encounter in the Eastern part of the Wastes. He is powerful and you should not attack him, if you haven't reached level 22-23, at least.
1) definitely, what is the most interesting in the Wastes are the tombs scattered all around the area. There are six of them. You explore the tombs during the "The Tomb of Fairel" side quest and there is a simple puzzle that you need to solve for each one. Solutions to the puzzles have been provided in the walkthrough for the game. I recommend that you take a peek into each tomb, because you can obtain rare items here.
2) Near the main tomb of Fairel, in the Eastern part of the map, you run across a great dragon. If your party is very strong, you can try and slay the beast. A very important piece of information, though, is that it is an optional thing to do. You can navigate around the dragon without any problems, on the North or on the South. An additional facilitation is the fact that he is sleeping and, as a result, he does not spot you sneaking.