I'd describe this game as 'solo, stealth mass effect'.

Solo in the sense that you are on your own. In some missions you will have allies on the ground and in all you have an audio link to your handler, but there's no concept of a squad. There are, however, a rich range of well-written characters you'll encounter on your journey. Many of the major NPCs can live or die depending on your decisions and this shapes the world throughout the game

Stealth is optional, but recommended. You can play every mission loud if you want to, but it might lead to problems for yourself or characters in the game. The stealth system is a little tough to start with. There's no charge-up time before NPCs start seeing you like in the Assassin's Creed series or Payday. However, after investing skill points in the stealth upgrade line and getting a feel for vision range, remaining unseen becomes a lot easier.

The Mass Effect series is the closest RPG I've played to Alpha Protocol in terms of overall design. Sure, one is an espionage game and the other is science fantasy, but beyond that they are quite similar. They feature an interesting, ongoing story consisting of a string of missions. In between missions, the protagonist rests up in a hub area where they can purchase items and choose which mission to undertake next. Gameplay consists of TPS action, interspersed with meaningful choices and hacking minigames. Choices in a mission can have a huge impact on subsequent missions.

The game does have its flaws: mid-lategame combat can be a little easy with certain skills, there are a few minor bugs lurking around and the story is a little generic in parts. Despite these issues, it's a great game that successfully manages to provide a good balance of action and dialogue. I'd strongly recommend purchasing if you enjoy both stealth games and RPGs as it blends the two genres excellently.