I'm not a huge Lt. Barclay fan. Yeah, he was never as obnoxious as Lwaxana Troi or Alexander Rozhenko. But the character was generally one dimensional to a fault.
The episode where Barclay ISN'T Barclay is thus more up my alley. The first half is a light-hearted nod at "Flowers for Algernon", as Barclay becomes a confident - even arrogant - genius who charms the previously unattainable Counselor Troi and does all sorts of other amusing hijinks. It's enjoyable and probably could have filled out an entire episode if the writers had been so inclined.
Unfortunately, they decided to shift to a "2001: A Space Oddyssey" mode in the second half, with Super-Barclay in HAL's role. I didn't find this part of the episode to be too satisfying. Others may feel differently.
Nevertheless, the best installment in the Barclay canon.