Total Recommendations: 4
Firstly, both novels were written by the same person, so it might not be a surprise that they feature quite some similarities. In both shows the protagonist enters a virtual world, in which they become strong characters. In both anime the protagonists face consequences in real life as well (related to the game world). I think SAO had a much more serious atmosphere, but if you liked one it's likely you will enjoy the other too.
Both shows are Key productions and are real tear-jerkers. Clannad probably makes you shed more tears, whereas Angel Beats! puts its focus on humor more often—but the end has just as much of an emotional impact as Clannad. In both shows, the characters are key points to the story. As for the setting, both shows take place in a high school setting. In short, if you loved one, you are very likely to love the other as well!
Both anime have a very strong sense of drama, and both stories feature an exceptional power to hit the viewer in the feelings. They can make you laugh, smile, and cry - as you find yourself to be in an emotional rollercoaster. You will probably cry watching both shows.
Both feature a battle royale setting, where several characters fight eachother to death for one goal. These characters are aided by a third party in both cases as well. This makes for quite a similiar atmosphere in both shows.