It's fair to say that this series wasn't well received by critics at he time, and I remember being underwhelmed too, especially after the superb third series.
However, after viewing the episodes several times they really began to grow on me, with many sketches being up there with their finest. Initially, I found the guest stars offputting and unnecessary, but Stephen and Hugh deserve credit for trying something new, and many sketches with the guests are hilarious.
So, don't listen to the detractors. This is classic Fry and Laurie and, whilst not being them at their peak, is still ten times better than most other comedy sketch shows.