I have a flat bar MTB I use in the winter and a road bike I use the rest of the year.
I've already stated what I like about drop bars but there is one thing I really like about the way my MTB is set up and that is the twist grip shifters.
The shimano STI shifters/brake levers you get on modern road bikes work fine once you get used to them but shifting by pushing the brake lever sideways is not all that intuitive. It takes some practice.
Also, these shifters traditionally been hard for people with smaller hands to use. Shimano has a good answer to this problem but what I can't figure out is why it only exists on their lowend shifters. Soras have a screw that let you adjust reach. It works great. On their higher end shifters you've got to buy these stupid blocks or get another set of shifters designed for people with smaller hands. Why is this? It's not a problem for me in particular but it's a problem for my wife. By lowering the height of the seat my wife could always at least ride one of my bikes in a pinch, but she can't ride my newer road bike easily because of the reach of the shifters.
Twist grips are dead simple to figure out, work well, and are cheap to replace.