The numbers were, as Roma Victor put it, "not pretty". Actually, the numbers were downright ugly. Take, for example, the cutoffs for the Bloodlust Battlegroup, the notorious BG9 where Arena participation has historically been intense. Last season, the top 235 teams in 2v2, top 92 in 3v3, and top 27 in 5v5 brackets were eligible to earn the Gladiator title. This season, those numbers dropped to 93, 36, and 8 respectively. That's a whopping decline in participation across the board in the most active Battlegroup in the US! ArenaJunkies also has numbers from Europe, Korea, and Taiwan and all of them show the same thing -- there are fewer players participating in Arenas than probably ever.
As cool as the new Deadly Gladiator's Frost Wyrm is, significantly less players are going to get it this season which is great for bragging rights but somewhat bad for the game as a whole. Roma Victor broke down the numbers for US Battlegroups and showed how much participation has dropped, with some brackets losing as much as 75% participation from Season 4 to Season 5. He also gives some of his thoughts on how to make Arenas more appealing to more (read: the casual) players. Considering that Wrath of the Lich King made the game much easier and more accessible, it's kind of sad that more players than ever feel alienated by Arenas. It's a truly ironic turn of events in light of how much effort Blizzard invests in that aspect of the game.