Don't let the bad reviews sway you. The metacritic rating for Alpha Protocol is 73/100, which is not nearly as low as the critics' bawwing would imply.
Don't put so much stock in the negativity, and check the game out for yourself. It lacks the polish that could have made it a true classic, which is an unfortunate trend with Obsidian, but it's still a great game...which is also a trend with Obsidian.
I've played 4 playthroughs so far and I've gotten a slightly different story each time. Even when I think "Well, this is where SIE is going to ask me to do this......" a totally different dialogue is given to me instead. Each choice really does affect the dialogue of future characters down the road. The game gives a lot of Catch-22 decisions where either decision seems to be right or wrong. Very intertwined storyline.
No, he's right, the game does have one ending, with variations. The sequence of maps and endgame cinematic are exactly the same no matter what.
There are a *lot* of variations though, in terms of how you handle the offer from Leland, who you choose as your handler, how conversations with various NPCs you meet at Greybox (Scarlet, Mina, Parker) go, and who the actual bosses are that show up at some of the designated boss fight locations (including the final boss fight) - it adds up to a lot of permutations. Also, many of the differences are based on decisions made earlier in the game or the accumulation of rep/dossier info over the course of the game, so you can't just save at the endgame and then see all the variations by replaying the last level over and over.