There really isn't much to spoil here, but honestly, Idk what the point of the episode was other than to shoehorn Lady Gaga in the plot.
And honestly, I like Lady Gaga, she is a great singer and one of my all time favorite pop singers, but I found it sad that she had to be in one of the worst Simpsons episodes. And FYI she was so excited to do this episode! I wonder how she felt once the episode actually came out and she watched it, if she ever did. They should have done a different plot with Lady Gaga and Lisa and it probably could have worked. My main problem with this episode is not Lady Gaga, it is Lisa. She is so unlikable in this episode and I couldn't STAND HER in this episode. She is so unlikable to the point that she yells at Lady Gaga later in the episode over...almost nothing. While her help attemps failed, at least she tried to help you, Lisa! Don't yell at her over stupid things. So she then makes Lady Gaga go off crying small diamonds and I don't get the joke. Why is she crying diamonds? And then she talks to Gaga again a couple hours later and then they do a song together. And then the episode just ends. However, I gotta say, the Homer Poker Face spoof at the end was kinda funny, which was the only thing i laughed at this whole episode.
On the other hand, Lady Gaga did a fine job voicing herself. I mean at least she tried. My other problem with this episode is they tell the same "joke" about her wearing weird outfits. Okay i get it! She wears weird outfits. You don't have to tell us 100 million times. Why can't you make up another joke for Lady Gaga?
Overall, is this episode the worst? To me, it is not number one but it is in the top 5 worst for me, on number 2. But I found Boys Of Bummer worse because it was like One Coarse Meal two years before it even existed and I hate episodes that joke about suicide, and especially when the suicide jokes are done horribly, also like FG's Brian's A Bad Father. This episode I didn't like because it was mostly boring and Lisa was so unlikable. The only good part of this episode is Gaga's songs, including the one at the end, and Gaga herself because she actually was somewhat likable in this episode, at least I thought so anyways. It doesn't mean it saved the episode from being bad though, but you know what i mean. I give Lisa Goes Gaga a 3.5 out of 10.