Joe -
I've seen O twice and really liked it. However, the first time I saw it my seat wasn't very good and I didn't enjoy it as much (the O Theater is a bit too big if you ask me).
What I would recommend is going to the Bellagio website and buying your tickets online. You can buy them up to 90 days in advance and can even pick out your own seat. If you can be flexible when you go, you can probably pick yourself out a good seat.
The prices, however, are a bit steep. I think they're up to $110 for the good seats. If that's too much, MYSTERE at Treasure Island is equally good if not better and the ticket prices are lower. Plus, pretty much every seat in that house is a good one.
Hope this helps.
Mike