I've done it twice but it was a few years ago so I dont know if anything has changed recently. When I did it, the first 50 mile loop around Lenoir was pretty fast but still had a few hills. After you go back through town, the bigger hills start until you get to the long climb up 181. It's not too steep but it is very long and there are some downhill parts there too. Takes a long time to get finally get to the parkway. The parkway is more of the same - mostly uphill but a little downhill to mix it up. You cross over 221 at some point and it can be a little depressing to see riders on that road knowing that you have to still get to the end of the parkway section before you even start the 221 section back to where they were. 221 is up and down and then you get to Grandfather. The first little bit of that isnt too bad but there are some nasty steep parts soon enough and It really kicks up right before the parking lot below the summit. After that part you can look up and see the switchbacks to the top and that can be pretty intimidating but the crowds at the top cheering and yelling can give you a little boost to finish strong up the last steep climb to the finish. It can be a little tricky holding it together while going up that road after 100+ miles with the cars and buses coming back down but it all seems to work out ok.
I've done it numerous times and if the weather is "cool" and clear it's a terrific ride. If it helps any, I usually finish BtB around 30 mins faster than AOMM.
I'm guessing with the later start this year (9am I think), they will not route us back through Lenoir at the 30 mile mark to avoid conflicts with the churches downtown. We'll head south from downtown Lenoir and then loop around back around the eastern and nothern part of Lenoir back over to Adako Rd and Hwy 181 like what was done 2 years ago. The majority of the climbing is the last 50 miles with Hwy 181, some on the BRP and Hwy 221 from Blowing Rock leading up to the entrance to Grandfather. I think it's 13 miles from the start of Hwy 181 to Jonas Ridge and then a few more miles over to the BRP. About 12 of those miles is uphill-nothing too steep but it's a climb that usually takes me around 80 mins to do. The first mile of Grandfather is not too bad. However the second mile makes you feel most every turn of the pedal. As Kostrikzer mentions the crowd gathered at the top really is a boost that helps you get up that last couple hundred yards.
The first time I did BtB I came up out of the saddle to do the very last climb and could not turn the pedals......I quickly started tacking up the hill and was able to get to the top without falling over. It's not the steepest hill you'll ever do but after 101+ miles it's plenty steep enough.
It is well supported and the organizers do a terrific job given it's a point to point ride. Usually there are a good number of people out cheering along the way in the Caldwell County Community.
If the weather is hot or rainy.......it can make for a really long day.