It's no so so tough as a general ride, but….
The concentration on the long long descents, followed by some steep climbing (on a hefty bike in clothing / helmet / armor wholly unsuited to going uphill as fast as you can!), all the while chasing / being chased by hundreds of other feckers.
The race is 1-2 hours (depending on ability etc), but if you were riding the course with mates for fun (i.e. not in the actual race), it's more like 3-4 hours – including plenty of stops for views / chats / rest. Just larking about in the snow usually takes an hour!
There's a couple of bits that will make most people think twice, but overall it's pretty doable.
I found riding the course on a hardtail in non race conditions was perfectly OK. The main line is fairly smooth – the Pros do take some ridiculous lines – especially in the qualifier – I doubt a hardtail would keep air in its rear tyre / a rider on board if you followed them!
I do think it's something everyone should have a go at at least once in their MTB lives. It really is a proper MTB race that attracts the whole gamut of MTBers – from proper Fat boys on their DH bikes to skinny race whippets, and the chance to rub shoulders (very briefly!) with the Pros, and the majority being the general weekend warrior 5/6inch mtb rider like, I guess, most people on this forum.