I was planning on commenting actually, like right now, I finished it a minute ago. Thanks anyway.
When Hacking to the Gate was played when the series got resolved it gave me goosebumps, obviously, but it's kinda funny that the entire point of the series was to resolve a plot device/deus ex machina in the original.
Personally, I didn't like most of the second cour(12-19-ish), because the quality itself drastically dropped, and the action sequences, particularly in the rooftop when the time machine is gonna blow up, were directed pretty badly. However, I did like a lot of stuff in the first cour, Okabe being PTSD ridden, and the introduction of other characters.
One negative point of this series is that whenever it tries to start an interesting sub-plot it fizzles out immediately, unlike the original which climaxed everything in a great way.
I don't really know what the OVA is gonna show, perhaps how the 2025 Okabe and others are gonna train Suzuha and convince her to go to the past and meet Steins Gate Okabe. Not sure. The original's OVA was necessary because even though the series itself resolved everything the relationship between Okabe and Kurisu itself didn't come to a close and it served as a great epilogue for that reason.
The post-credit scene was sick for sure.