I've only started watching it again recently, so I can't say much on the subject. Review subject to change.
I remember watching this when I was younger, and I had good memories of it, so I wanted to watch it again. But most streaming services don't have Sonic Underground (as far as I can tell). I know Amazon Prime features the series, but it costs about £40 for the whole series. It's good, but not THAT good! Paramount+ has Underground, but, since I live in the UK, it's not available until June. Hopefully, I can find it on there.
Sonic Underground has quite the plot. We all know it by now. It sucks that this series didn't get a proper conclusion. People complain that Sonic Underground doesn't relate to Sonic in the sense that he now has 2 other siblings and a long lost mother. Think about this series as it taking place in an alternate universe (or not as a Sonic programme), and it gets a bit better.
Honestly, the songs are the best part of the programme. I can't count how many times I've listened to the theme tune on repeat. It's amazing!
The way the characters are portrayed is good. Sonic is his classic self; he has his signature speedy trait, he's hydrophobic, and his confidence levels are through the roof as always. Manic is similar to Sonic, although he hasn't got the confidence or the speed that Sonic has. Sonia is, probably, the most mature of the three. Seeing as she was brought up in a royal household, it does make sense that she's the mature one of the three siblings.
This review is subject to change, as I haven't been able to watch the entire series.