What was her last great album?

[Cheshire-B]

it's glory, of course !

[itswwasheembitch]

Music wise: Glory

Commercially: Femme Fatale

[Lex993]

Glory and we’re not going to act like that album isn’t great because y’all want to get amnesia seven years later. 

[agustinmalandra]

Glory. before that, Blackout.

 

FF is cohesive but somehow it sounds fake. Myah Jean is a crime to our ears and Circus is not cohesive yet nice.

[GregReid]

Glory, I feel more comfortable listening to it too knowing it was more of her 'baby' and she wasn't forced the way she was with FF. Let's be honest!

[2K16NEY]

Glory was a great Britney album. You can tell her heart is in it.

[stanLOONA]

Blackout (2007)

[G-unit]

Glory.

I don’t think FF aged very well and it sounds very uninspired.  I like the album, but it’s possibly my second least favorite album, behind BJ just because it does seem very void of real connection from Britney.

[Alvy]

Her last GREAT album overall is Blackout. No doubts on that.
Since Circus everything seemed just desperate attempts from her team, BUT Glory is kinda great but not that GREAT you know what I mean? like, the album is the only post-Blackout that seems more like her in a "mature" way. 
But if you ask me about her LAST SUCCESSFUL album, that'd be Femme Fatale.