I dunno. Looking back and after watching shows like Brave and the Bold I kind of find myself not really like liking Justice League all that much. Im not saying it's bad, it's actually quite good. For the most part. But there's a lot of little things that rub me the wrong way and one or maybe two big things.
Mostly though it's just so bloody series. Not Snyder serious but closer to Bat Man TAS serious. Which given Timm's involvement is hardly surprising. There's certainly no shortage of levity either but everything as a very dire overtone to it, that I don't know I always like.
But that's really just me being a jerk, no my only major complaint is that Timm either seems to actively hate or just doesn't get Superman. He's very much one of those "How do we make Superman more relatable, Oh I know let's make him a jerk." It was reigned in during Superman TAS which is a show I enjoy and suspect he had other writers doing the heavy lifting. Yeah I get he's the big blue boyscout and he's so strong he can solve every issue alone but that's hardly an excuse to write him like a jerk or gimp him just to make Batman look good.
Also I don't like his character designs. Everyone's got the same build. It bugs me more than it probably should but it bugs me a lot.