What a letdown. It had been humming along nicely, the story developing and you gaining experience points and stuff. Then you kill Vaas...... and then bing bang boom, like three missions later you kill Hoyt and the game's over. It was totally anti-climactic, and it had the distinct feel that whoever wrote the story simply ran out of ideas.
I did sort of dig the idea that you could kill your friends and join Citra, or you could choose to spare your friends and leave Citra. That was a cool twist (I chose to leave Citra, but I watched a YouTube clip of the other ending..... whoa!) in what was otherwise a stupid ending. The doctor simply disappears from the story despite being setup as a fairly important and interesting character early on only to be killed off-screen by rampaging Rakyat warriors at the end. Vaas was clearly the badass despite being an underling and they inexplicably kill him off 3/4 of the way through the game instead of making him the final boss battle. You meet the utterly useless Sam who serves no real purpose in the story; there's literally nothing he does that he and only he could have done, thus requiring his presence in the story.
Then let's consider some of the bigger shortfalls: The heroes are very badly written..... they're a collection of jerks, and do-nothings that I'm not sure anyone would risk their life trying to save. The more skills you get, the more guns you unlock, the more stuff you can do, the more restrictive and linear the missions become. The missions after you kill Vaas are seriously stupid.
Honestly, the ending is so bad I feel like I can't recommend the title to anyone who wants to play SP.