I'm not going to tell you the specifications of the High Roller since most reviews already have told you that the 550 foot observation wheel is currently the tallest in the world.
I recommend riding at night versus the day since you really get to see a stunning view of the entire Las Vegas Valley. For the people that love airplanes, at night you can see the landing and take-off patterns into and out of McCarran.
Before going, check if Groupon or Amazon Local has a ticket deal.
Also if you have a Platinum, Diamond, or Seven Stars Total Rewards card, be sure to first stop at the Concierge Desk. Depending on your card level, you may be entitled to a larger discount or free tickets.
A word of advice for locals: Present your Nevada ID and you get a $5 discount.