They are extremely comfortable and light.  The last 2 pair I had were the Wave Alchemy and I think I may like these better. 6'2. 215lbs with no arch at all.  I usually run about 3-4 miles 3 or 4 times a week.  I've put about 40 miles on these so far and no complaints.

The last 2 pair of Mizunos fell apart earlier than other shoes I've had.  I'm hoping the Nirvana's hold up better.