While it's mostly for harcore fans I'm a casual fan, it works for me big time!
It's got technical stuff: Most people say this game is for the hardcore f1 fan, or the hardcore racer fan. This is true to a certain extent, because there are lots of technical things that you need to understand. For example; aerodynamics and car suspension. Car assists such as braking, traction control and automatic gear changing help the inexperienced driver to stay on the track and be competitive against the AI on Easy mode. Anything higher though and you will need to drive without assists. On top of that, knowing the tracks are a major part of being successful.
Single Player: The games career mode is immersive, with full practice, qualifying and race sessions all available depending on how much effort you want to put in. You can adjust the realism depending on the challenge you want to set yourself. Fuel, tyres, race rules, and different race lengths give you the chance to set things how you would like them.
Multiplayer: You can play with a friend in a co-op career mode which offers the same as the single player mode but with twice the fun provided you have that reliable friend to play with. Other online modes include 3 lap races, grand prix sessions, and 20% race length endurance sessions. Those are fun, especially if you know the tracks how to drive without assists - all the good drivers do. I'm happy to compete further down the track for now, there's always someone on your level in an online race.
Time trials: Proving grounds offer time trial style challenges. They do what they say on the tin.
Other stuff: Basically, the presentation, graphics, driver AI is great as far as I can tell as is car handling.
Summation: It's how I see it as a relatively inexperienced driver. There's nothing more exciting than feeling like you are on the edge, driving to your limits in the fastest thing on four wheels. Beating another driver by mere tenth's or even hundred's of a second is fantastic fun. The satisfaction increases as you increase your difficulty level, remove the driving assists, and up the race realism.
Buy if you think you would like to experience the excitment described above.
Don't buy if the potential challenges are too much for you.