Based on my few experiences, I would give Mitchell's a 6/5* if I could--it's just that good!
The atmosphere is very fun and inviting. They have a good system in place regarding the ordering process. Plenty of people behind the counter are ready to assist you in sampling flavors or making your order, which keeps the line moving quickly.
There is such a large variety of treats and flavors to choose from. The portions are very generous and you can tell that their ice cream is high quality! My hot fudge sundae tasted incredible last week--I love their whipped cream.
I strongly recommend Mitchell's if you're craving ice cream from somewhere other than a chain.