Tony, I think you're giving up a little too soon. I, too, was curious about Haagen Dazs Five, and luckily started out with the "Passion Fruit" and "Ginger" flavors. These were quite good, had a very smooth (almost frozen-yogurt like) mouthfeel, and have bright, natural flavors. "Lemon" is also good.
I had a very similar reaction to the Brown Sugar. I had several bites but actually couldn't bring myself to eat the rest of it. I was extremely disappointed; I'm a big brown sugar fan, and had high expectations after trying those first few, yet I agree with you on all points. Boring flavor, and most surprising was the odd mouthfeel. I'd give some of the other flavors a chance; in my opinion, the "mint" and "vanilla bean" are unremarkable. Haven't tried "strawberry," "milk chocolate," "caramel, " or "coffee" yet, and I don't know that I will. But the first three I mentioned really are worth a try, if you have the budget to splurge on ice cream experimentation. Don't give up quite yet!