The closest to perfect I've seen a game come to since Final Fantasy VII
In Mass Effect, the storyline plays out based on your words and your actions. So say that you would love to help the person out and be there for them or do something just, you will get Paragon points. However, if you tell them that they are full of it and can go shove it or do something unjust, you get renegade points. It's extremely similar to the Light Side-Dark Side of Knights Of The Old Republic. This makes the game definitely worth replaying, just to see how different responses shape the story.
The combat system will make the game feel more like a third person shooter than an action rpg. But that will quickly change in the latter parts of the game, when things get a lot more difficult and require you to use some strategy or techniques than just shoot. Depending on which character class you make Shepard in the beginning of the game, you could have a wide array of physic abilities at your disposal or make him a just a regular point and shoot soldier. But don't worry, there will be characters in your party that will have access to these abilities.
The only downside to the game is the driving portions where you have to navigate the map via a land rover/tank. To move and shoot accuratly is extremly difficult and borderline near impossible, so you would have to stop or slow down to accurately aim at yor target. However this makes you a sitting duck and will suffer some heavy damage.
This game is one of the greatest games i ever played and i'll recommend it to everyone. Now all i have to do is wait for Mass Effect 2 to come out.