It's nothing of the kind. The game mostly consists of totally untimed classic adventure-game type investigation sections, with (generally optional) rockstar style freeworld roaming segments in between, and occasional action segments (car and foot chases, gunfights).
The investigation elements are in theory interesting, with some nice (if simple) puzzles. Most of the time you're just canvasing areas trying to find clues, which will point you towards new locations and people, and help you in interrogating said people. This doesn't just straddle the line to boring, but sometimes also crosses it resoundingly. Mostly the areas are quite bearable, but occasionally they are a bit on the large side, with a lot of wandering required. I can live with it, though and it does have a certain addictive quality to it.
The much-touted facial animations play a big part in the interrogations. Unfortunately, anyone who complained/complains about the Mass Effect dialogue wheel is probably going to have their head explode here. You ask a question, the perp/witness answers and you get your choice of truth (believing them)/doubt (essentially accusing them with proof)/lie (proving that they are lying with a clue from your notebook). In practice, in a lot of situations you can tell that the person is avoiding telling you something, but it still might be truth (they didn't tell you everything), it could be doubt (which it basically should be) or lie (with some pretty serious leaps of fancy being necessary to connect the proof). The core problem being that especially with "lie", your mouthpiece can take the interrogation in an unforeseen direction, and the proof you had turns out to be inapplicable (for that particular question). Or just completely unforeseen in general.
You can skip the driving around almost completely (you can let your partner do the driving), but sometimes this will results in different situations at the next location (say, gunmen might have escaped due to being too slow) or a clue not showing up. I found the driving to be generally a LOT better than in the last Rockstar game I played, GTA IV, both in physics and in camera.
Story-wise, it's a typical on-rails story, where nothing you do impacts the story in any way, and includes a lot of failed story-failure. Trying not to cross into the spoiler territory, but sometimes the game doesn't allow you to reach the correct result. Sometimes your character just makes decisions for you that I find grating I dunno, I've gotten this feeling in a few games over the couple of years, mostly this one, uncharted 2 and Brutal Legend, and I can't quite place it. Lack of the famous RPG elements?
Mostly, I enjoyed the experience, but found it to be fundamentally flawed as a game. I don't think my issues with the interrogation mini game were due to an inherent stupidity on my part, but it is, of course, a possibility.