Ichigo's bankai doesn't have the power to increase his speed or power or anything like that. All it actually does is play his theme song allowing him to win battles he should NEVER have a chance. Aizen just turned off that goddamn song and he was helpless.

Random fun and useless facts:

Welkin Gunther (Valkyria Chronicles) shares the same Japanese seiryuu as Isao Kondo (Gintama). While Welkin Gunther and Pain (Naruto) momentarily shared the same English voice actor.

Sasori (Naruto Shippuden) shares the same Japanese seiryuu with Faldio Lanzaat (Valkyria Chronicles) and Izuru Kira (Bleach). While Sasori shares the same English voice actor with Ichigo Kurosaki (Bleach).

Not surprisingly, Radi Jaeger (Valkyria Chronicles) shares the same Japanese seiryuu with Kyoraku Shunsei (Bleach)

Emilia (Blaze Union, Yggdra Union) and Pamela (Blaze Union, Yggdra Union) both share the same Japanese seiryuu.

The sisters Aegina, Luciana, Yggdra (Blaze Union for all 3, Yggdra Union for Yggdra) all share the same Japanese seiryuu along with Hatsune Otonashi (Angel Beats!).

Garlot (Blaze Union) shares the same Japanese voice seiryuu with Szayel Aporro Grantz (Bleach), Himuro Saeki (Hayate no Gotoku), and Kiba Inuzuka (Naruto Shippuden).

Kagura (Gintama) and Sanzenin Nagi (Hayate no Gotoku) share the same Japanese seiryuu.

Sakata Gintoki (Gintama) and Kyon (The Melancholy of Haruhi Suzumiya) shares the same Japanese seiryuu to the point where the former parodies the latter.

Yui (Angel Beats!) and Akeno Shurinai (Seto no Hanayome) share the same Japanese voice seiryuu and currently waiting on official news whether or not Arecia (Blue Roses: Yousei to Aoi Hitomi no Senshitachi) also does as well.

Katsura Kotaru (Gintama) and Gaara (Naruto Shippuden) share the same Japanese seiryuu.