Google Drive is one of my favorite tools (in case you cannot tell). I love that it limits the paper use in my classroom, encourages collaboration, and allows me to give more meaningful and substantive feedback. One of my favorite features is the ability to provide vocal feedback via the third party application Kaizena.
Kaizena has just had a major upgrade/overhaul that makes it more stable and substantive. It also plays nicer with firewalls (so you can use it on campus). Kaizena allows you to login with your Google Credentials (no extra passwords). You simply highlight a section and record (just like leaving a traditional written comment).
One of the new features that I like is it allows you to attach a lesson or a video to a common problem – if you notice students struggle with a concept (such as formulating an effective thesis), you can simply attach an established video that you use to help clarify it (Kaizena will even remember that you do this). Such a time saver! If you would like to learn more about their updates, you can read their blog here. You can check out a demo of Kaizena (the older version) below: