The New Avengers attempted to resurrect some of the old spark that made the original Avengers so great, but the changes they made ultimately killed any chance the New Avengers had to succeed.
On the positive side, Brian Clemens returned and wrote some solid, if flawed, episodes to start off the series. In fact, the pilot is arguably the best of the series. The off beat stories, such as reviving a Hitler in suspended animation, were reminiscent of the original Avengers, and of course Steed was back. The episodes also featured some of the old Avengers' humor.
On the downside were many. For one thing, Steed's character was deemed too old to be fraternizing with young women, and they wanted "romance" so they added a new male character who was essentially a Giglo. He lacked the charm of Steed and seemed to have a distinctly American feel despite being English. This was the biggest problem with the show. It was far too influenced by American shows from the 70s and too little influenced by its source roots. For example, car chases (rare in the old series) were plentiful in the New Avengers except that the directors were not very good at it. It was literally like watching 5 minutes of cars turning corners and knocking over a fruit cart every now and again. Another example was the influence of the studios which wanted the New Avengers to film on location in Paris and Toronto. All of the sudden the Avengers were world travellers helping out foreign countries! Another problem was Steed's sudden attraction to guns. In the original series Emma and Steed almost never carried guns. In the New Avengers guns are common place and Steed even shoots several people! Sadly, the biggest drawback was the rapid decline of quality scripts. The early episodes were not bad despite the aforementioned problems, but many of the last episodes were downright boring. Even when they had a good idea, it backfired. A prime example of that being "K for Kill." The story was great, but by stretching it into a two hour episode, the second part was plodded and padded to the point of boredom. It might have worked great at one hour, but at two it just didn't work.
In short, fans of the original Avengers may want to try this, but it may leave a bad aftertaste. It is still better than many shows out there, but compared to the original it a pale imitation. Give it a try, but don't expect too much.