Britney has been going through a very difficult time, and has been overwhelmed with pressures & obligations.
I doubt any of us could have a year like she's had, and then just jump up on a stage and WoW 'em.
She has given better performances in the past, ...however, with enough prep time, discipline and dedication,
she can deliver a performance that few will be dissappointed in. Hopefully she will hit her stride again soon.