I think it is a good thing for the official applications to all feel and work very much the same. However, for obvious reasons long-time users of Twitter may feel the changes are a bit jarring. John Gruber rips into Twitter for iPhone by comparing it to Tweetie (which is what the application started out as). Mike Rundle rips into the app on its own merits.
Some TweetDeck users seem to like the update since prior to this latest version the application was a horrible Adobe AIR application that (at least in my experience) was slow, poorly designed, and bloated. This latest version seems better.
I don’t use Twitter for iPhone or TweetDeck and I only use the Twitter.com website on rare occasions. I’m very, very happy with Tweetbot.