So first up you need 3 crypt keys just to enter it. That's right, I did not misspell that - it is a huge cost of 3 crypt keys and only for entering without any guarantee of a worthwhile reward especially for those entering for the first time.
The bosses get really hard really fast, far from what it's like in the catacombs. There are 30 levels but most people will never get even close to that. Don't even bother to waste 3 crypt keys unless you are very strong already - definitely over 40k br, but probably better above 50k br for the first time.
Boss 5 is important for being able to buy high level items in cata shop, but there is no great reward to speak of; the chance for level 4 gem is low as you can imagine. And passing boss 10 which is the next big step requires an extreme amount of power, which means you would have to be one of the top people in your server most likely.
So here we have the video I made where I pass level 5 and die on 6:
And here is the video of DvDpC who is having fun passing level 10 on AFK mode - that monster! :)