I just recently re-installed Alpha Protocol. It's such a great game, probably one of my top 10 picks for 2010, yet it was hated by game critics and therefore got put in bargain bins way too early.
The gameplay is mostly third-person shooting and some sneaking; it plays a lot like a slightly blander version of Mass Effect 2. There are also a few minigames such as hacking and lockpicking that are tolerable, yet not too much fun. I've also heard that some people encountered bugs in the game, though I personally didn't see any.
Where the game really shines is on the story. The game was developed by Obsidian Entertainment, the same guys that did Fallout New Vegas and Neverwinter Nights 2, so you know that even though the game might be buggy and have some questionable design choices, you'll always be treated to a great story. Basically, it builds up on the standard spy fiction thriller tropes, yet the story remains solid all throught the game.
My favorite part was the choice system. Much like Mass Effect's three standard choices, you can choose between a "Professional", "Suave" or "Agressive", basically the game's way of making you choose between "Jason Bourne" "James Bond" or "Jack Bauer", in that order. The best part is, almost all your choices will have important ramifications during the course of the game. Where in Mass Effect the conversation options led you to the exact same place in the end, there are wildly different outcomes depending on your choice, and they all make sense in the game. The cohesion in that sense is very interesting.
The game is like $15 on amazon right now, definitely a steal for such a great game.
(Oh and by the way, the first few level take place in Saudi Arabia and are a bit boring. Trust me, it gets much better after those few levels.)