I'm not impressed. It is definitely better than the stock browser which is horrid - lack of features and loads extremely slow. However when compared to my daily browser, Opera, it feels gauky.
Compared to opera it loads just as fast, displays flash just as well, webpages look just as good. But the app itself just doesn't look good.
Dolphin has the tab bar on top, which makes it easier to access, but it isn't done well. I would rather have them remove that and use the tab page they have that is similar to sense previews. It takes up too much space and is IMO ugly.
The guesture menus are a great idea. And they are easy to bring up. Again, however, I don't like how they look. Either they should take up the whole screen rather than just part. Or have a transparent background so that they are "overlaying" the webpages.
Also, I had it FC on me a couple times while loading pages and changing settings. Not an issue for me as its beta.
The one thing I really like about it over any other browser I've used it that you can change the user agent in settings easily! Opera you can, but you have to edit the opera:config and its a pain.