A HINT of nervousness (only to be expected on the first night), a few puppet-like movements and a marked absence of off-the-cuff chat with the audience, but otherwise a very entertaining and enjoyable show, marked Herman's Hermits' opening at London's Talk Of The Town on Monday.     Clad in a black velvet Edwardian suit, while the Hermits were in grey, Herman began with "A Kind of Hush", then went into "Sunshine Girl," which included a comedy take-off of "A Scottish Soldier." Using the ample stage to advantage, the group presented a hits medley which consisted of "I'm Into Something Good" (their first hit five years ago), "No Milk Today" and "Something Is Happening."     A surprise came during the romantic "Love Is Blue" when Herman produced a flute and played a few short chords, Keith Hopwood switching to acoustic guitar and Barry Whitwam sitting at the front playing bongos. It was certainly one of the most well-received numbers of the evening.     Introducing a selection of Inkspots' songs, Herman announced - "This is a group we think were fantastic although we never saw them work on the stage because we weren't born." They codded it up and drew a lot of laughs with their fooling about and voice changes.     After Jack Jones' "Without Her," perhaps the most successful song was "If I Were A Rich Man" which came during a selection of songs from current London shows. While Herman stood on two stools, the Hermits skipped around him banging tambourines. At the end, Herman leaped over a mike stand and received long and loud applause - deservedly so.     I expect he has received some coaching from his wife for "What Now My Love," which he sang partly in the original French form of "El Maintenant." A false close then they all came back for "Henry The Eighth," on which the audience were invited to join. It took a bit of doing, but in the end quite a number of people were singing along.     Nobody could expect the completely professional performance of, say, an Orbison or Bennett, but Herman's Hermits were well-rehearsed and impressive.