I texted my BIL who lives in Dover, NH, and he says Black Trumpet Bistro is his favorite restaurant in Portsmouth, FWIW. He's in medical sales, and often takes doctors/hospital administrators out to dinner. Says this is his go-to when working close to home if he really wants to impress a client. Heard of this place, PTR?
I also second the Ri Ra Irish Pub recommendation. I've been to locations in Burlington and Charlotte, NC. Excellent Irish food, great beer selection, and cool atmosphere/decor. Makes you feel like you're in a pub in Dublin.