Anime First: Anime -> Manga -> Second season. As a result, some ideas from the (considerably darker) manga end up in the second season.
The second season was then followed up by more Manga (unreleased in the US), with the purpose of tying up the manga continuity with the previously aired season.
No Export for You: The second season has seen no release in European territories, and probably never will since Beez Entertainment has gone the route of its parent company and stopped distributing animé titles.
Screwed by the Network: Despite that it was a popular show and the ratings of [adult swim] airings were the sole reason the series even got a second season in the first place, the premiere of the second season was around the same time Adult Swim began its Network Decay, and they ended up screwing up the airing of a couple episodes (including accidentally airing a repeat over the finale) and ended up canceling the show before a reportedly expected third season, despite it having paid off financially.