A somewhat disappointing kick-off. I admit that I messed up by starting with the second entry in the series, but that shouldn't excuse the poorer quality of this first installment. The problem with Slum King is that it's a lot tamer than its follow-up. It's mostly just an introduction to the setting with some mild violence to fill in the gaps.
The art style is less detailed and the animation isn't quite as energetic. The characters aren't as crazy or over-the-top either, giving it an overall cheaper feel. While there is still some gore and weirdness, it never makes much of an impact. It's still amusing to watch though, but it's really hard not to compare it to the much better second part.
The comparison may be a bit unfair, on the other hand I'm not sure if I would've continued with this series if I'd seen Slum King first. It's not terrible, but it is quite underwhelming and apart from a handful of solid moments, it's too cheesy and forgettable to make a lasting impression. Persevere though, because it gets better after this.