Yeah I'm just gonna say, I did like the characters and idea of the whole thing, but in the end I felt the anime kinda left me to be desired. And just like you said, it's because 13 episodes was too little to flesh things out.
This is just like Angel Beats and AIR. Both of those needed more episodes to flesh out more of the material. I didn't like how it just felt like they skipped all the potential character arcs in Angel Beats at the latter half with just a half-assed reasoning for all of them to just suddenly move on so easily, and I didn't like the pacing of AIR compared to the amount of source material they have in the VN apparently, especially with the other character routes.
I guess that's why I absolutely loved Kanon 2006 and CLANNAD. He had twice as many episodes to adapt the VNs into an anime and I think he gave the characters sufficient time to connect to them more because of this (Kanon 2006 is still my current absolute favourite anime, bar none). They really need to give him another 26 episode slot for him to work with.
Btw, I know it's minor and cheesy as all hell, but I did really like how the final power Yuu discovered was the simple power of courage. It made me smile at that and I thought that was a good way to end that "arc". Still gonna watch that OVA though!
EDIT: Then again, I was one of the people who watched it as it AIR'd (heh getit? :V), so maybe my experience with the anime varies greatly with those who binge watch it? I binge-watched the other Jun Maede anime so maybe that's why I thought anime like Angel Beats were so much better.