I had no idea it was popular to hate Gotham. I never heard of its existence before it appeared recently near the top of Netflix, where, because it's named Gotham, I figured it must be a Batman thing. And I like Batman. But in retrospect, because it's in the Batman universe, I can see why comic book nerds have strong feelings about it, being possessive and picky as they are. Just like with comic book movies.
Now, I want to be clear. It's not great. It's barely good. First of all, it has children actors in prominent roles with a lot of screen time. One of the things I do like about it, is that it pulls this off so well. As well as can be expected, I mean. And I think they manage to not ruin it only because they are older children, probably well into their teens. Secondly, the writing really is pretty bad. It's completely formulaic and cliched, and kept within a narrow band, so as to appeal to the widest possible audience. But, what it does really well is immerse the viewer into the Batman universe through its production design. The police station set is a great example. Perfectly captures the feeling of the comics (as I remember them, from a million years ago).
Who's supposed to be the young Joker? The circus kid, who killed his mom? I can't remember. I thought he was only in that one episode, and laughed like the Joker once, and that was it. Maybe I slept through a couple episodes around the episode 15 mark or something. And what you're saying about the finale, I know for sure I watched that, but can't remember the things you're mentioning. Because, ultimately, that's the thing about this show. It's all visual style, and otherwise completely forgettable.
Ultimately, I think the number one thing that kept me going with it, beyond the Batman branding (which I will admit attracted me, and I'd probably never have watched it otherwise, so I'm part of the problem in Hollywood w/ sequels and reboots being the only movies that get made anymore--watching something only because of familiar branding...), is the one really good and strong dynamic in the show: Gordon and his partner. They're great together. They even have a good arc that moves over the whole season, where Gordon gets increasingly defiant and determined, and Bullock's (Bollocks? what's his name? ha) heart grows three times larger, as he starts to care more about doing the right thing a little more each episode. That was done well.