its one the the major annoyances i have when upgrading MC, all your views get screwed over with new columns added into all of them (eg most obvious fields are rating and genre, they keep getting put back in every release - hint, i dont want them which is why i removed them please stop putting them back in)
you can re-customise the view and remove the "large icon" field (to get rid of the album art).
i actually dont mind the groupings too much but you can get rid of them easily if you dont - go into View > Customise and change the grouping to None - should now be back the way it was in MC12. note if you change it back to album grouping youll get the large icon back (just remove it again)
not sure why you have to load the music folders again, it should be fine if you used the same library from the previous verion