Just watched the second half of the series myself.
Overall, I liked the show quite a bit, but I'm definitely in the crowd that thinks the show peaked with the first four episodes. Nothing since then has really been of the same quality, despite there being some moments of quality.
Characters were likeable enough - Satoru, Kenya, Satoru's mum, Kayo etc were all characters that I rooted for. Satoru's mum is the peak though, absolutely.
On Airi - I liked her too, the problem with her was - and by the same token, the problem with that final scene - is that she pretty much adds nothing to the series past the halfway point. Hell, the timeline that the series ends on literally has nothing to do with her bar that final scene.
Don't get me wrong, I like that she and Satoru will have a chance to renew their friendship/relationship/whatever, but it didn't feel as earned. This is especially apparent after seeing the fates of characters who were actually present during the second half ot the series.
It also doesn't help that the last major bit that involved her character was a pretty silly story about chocolate bars. That's going to colour the perception of her since she didn't have a chance to do much else. Shame really, because I liked the scenes with her and Satoru in the first half. Ah well, I hear things are different in the manga, I guess Airi is just a victim of the distillation.
The whole rooftop conversation with Yahsiro was weird too. "You can't live without me" didn't feel as earned as it probably should have - kind came off as trite in the end.
So yeah, I think it can be safely said that Erased is a good show. Hell, it verges on the excellent for the first third of the series. After that though it stumbles and never really regains the same footing. I recommend it, but I completely understand if people are disappointed with the conclusion when one considers the quality of the opening.