Personally, I find that counter-intuitive in a WIMP UI. If it keeps happening, you can change your double-click speed in System Preferences - shortcut key is Enter (which has been the shortcut since before Windows or Gnome/KDE existed). File extensions have always been hidden by default. Again, on a WIMP based UI, they're kind of superfluous. Finder is super snappy form me. Literally just launched it and it's there straight away. Obviously YMMV...