After download (windows installation is 5.6MB) it install smoothly, without any problem with extensions etc.
However, my first impressions are not very good. I simple don’t like new default theme, something simmilar as “Go” button is added next to location bar and search bar, there is no longer close button to the far right side of tab bar, now you have close button added for each tab (like in Opera).
About new features, now firefox is able to remember your session (reopen all tabs you had before you’ve closed it). On my machine it is not enabled by default, but it can be easily turned on in ff options. Also, there is a new spell checker which is enabled by default with english dictionary. Very annoying if you mostly write in non english language, and don’t have dictionary support. Search bar is now able to list you suggestions soon after you star typing your keyword (simmilar as Google Suggest tool).
Regarding new options in menu, I haven’t noticed many changes. In History part there is a “Recently closed tabs” option, very usefull especially if you’ve closed some tab by mistake. Also themes and extensions are now reorganized under “Add-ons” menu, which is part of Tools menu. In Options menu there is a “feeds” tab where you can define how would you like to handle rss feeds, and in case you don’t have any feed reader installed, you can pick some of online readers (like Bloglines, Google Reader etc.).
All in all, I really liked ff 1.5 look and feel much more, but FF 2.0 have some interesting new features. Will give it a chance for a few days and see if I am going to keep it, or revert to goof old FF 1.5.x.x :)