I liked the 2003 series, although it took a few episodes to grow on me – I wasn’t sure about the silliness and I especially disliked them hopping on the tail end of the “let’s throw anime elements into traditional western animation” bandwagon. In the end, though, I think the balance of serious with emotional with silly made something special.
Compared to that, TTG was definitely not as good in my book. I could understand the context, though. After JL/JLU, Teen Titans was definitely a bit silly. Then came Young Justice which was definitely serious again, but maybe a bit mature for the kids. Then we swung back to silly with TTG.
Anyway, to cut to the chase, I took Go! for what it was, and I did really enjoy it for a good while. After two or three seasons, though – I don’t know if the writing started changing, or if the novelty just wore off – but I started finding it less enjoyable on average. I still watch on occasion if there’s a new episode, and every once in a while I’ll find one hilarious, but they seem to be getting fewer and further between.