I missed in old versions, however, such as I do in 1.7, small things which for a few people are really important.
1) Tagging is painful; these guys in our websites do work intensely in writing news, so they do in an internal system and then copy and paste contents for different fields in each item. As tagging (or in the old way keywording) has to be congruent to provide a good related-grouping, they select keys in their own system, and then copy all the block with comma values and paste. They hate K2 tagging, one-by-one, being such a slow method. So they go to keywords pasting in the old good joomla basic system. It's faster, it's reliable.
2) As we're running different websites, we've hosted all pictures and media files in a big 'materials site', where they are FTP uploaded: I'll not describe the full internal system, but in joomla we paste the url for pictures and so. In K2 you've to upload each picture, one by one, to same website hosting server (or you could FTP them and then selecting manually one by one). Only in case you have internal pictures within the news (not the main one), they can be pointed to an external url address.
So, if you don't need these kind of small things (which in our case do increase a lot productivity, but probably you'll not work in this way), K2 is really big.