It's not an easy one to answer, because BTW is a big seller and all her singles have been in the Top 10, apart from 'You &I' so if you see it from that point of view and compare it to other female acts like Rihanna, Katy Perry and of course Adele, she's been doing well with her album, firming her status of the most popular pop star for this new generation and leading this era of Music when it's as much about the music as it is about being the darling of Facebook, Twitter, Youtube and any other social network that can get you adored by the one 'like' click.
Now if we put it back to a certain perspective, I think she's been struggling with this era. I'm pretty sure she wasn't expecting such lukewarm reception at any levels. True, Charts positions and sales are not all but when she released BTW, she had the world in the palm of her hands and there was so much anticipation for the album that it should have sold at least the double it has sold by now. I know the album sales are in decline but that doesn't explain why she hasn't done better.
To me it's simply down to her (and her label/management) - she/they got really complacent with the strategy around the album. I feel with The Fame/Bad Romance era, there was some consistency in the way the album was promoted, the image she was creating and the themes in her videos. BTW, from that point of view is a complete mess. It looks she/they tried to be inventive in the promotion strategy and it didn't really work. As for her videos, they became more and more predictable and lost the impact they first had on the general public/media.
The BTW single debacle may have been more decisive than anyone thinks. GaGa has always been compared to Madonna since she first came out and, if anything it seemed to play at her advantage for whatever reasons, but this time, it clearly backfired at her. The fact she came out with a message which was that dated was already a bit of an issue but the way she handled the whole controversy, with false claims about Madonna's personal email sent to her, using the 'R' word in the NME's Interview followed by a clumsy apology has probably left a more negative impact than fans and perhaps even her are keen to believe.
Creatively and musically, I don't think she has delivered either. As I said earlier, her videos are now way too predictable, not that much entertaining nor interesting than other music acts and she seems now to have fallen into that trap where everything she does has to be for her 'monsters' instead of doing what she personally wants to do and let the fans embrace it naturally. As for the sound of the album, I don't agree it's not that commercial. Perhaps to Radio 1 standard, her singles off would be too avant-guarde to be played on a bright weekday morning but BTW is pretty much a Pop album with darker tones and slight different influences than TF and has enough radio-friendly singles to rule the radio playlists - I remember when Hair and TEOG were first released, they got picked up by Radio 1 and Capital straight away - so certainly the poor choice of singles and handling of their promotion didn't help the situation (i.e. I don't like 'Hair' but for the message it conveys and how the song experiments with different arrangements, it would have done better in terms of impact and publicity I think than BTW which was plain, patronizing and so dated).
Also we have to consider why the likes of Adele, Katy Perry and even Beyonce have caught the attention over LG since their albums came out at different times. Doesn't matter if one thinks Katy Perry is a singles artist and rubbish, the fact is she has matched MJ's record with a 2nd album which is now a long player. Adele has totally overshadowed GaGa with an album which was not that anticipated and , in my opinion, wasn't that commercial either on paper. But in these comparisons, Beyonce's case is the most interesting. She came back with an album which is seen as not being commercial, with a lead single which fell flat and yet she took the world by storm with a couple of performances at Glastonbury and the VMAs once again outshining LG.
Whatever she's aware of, I feel she has now a point to prove - and it's not necessarily about being different from Madonna - which is quite ironic considering she has built this era on trying hard to prove many points which were quite frankly irrelevant.