Each series plays out like a NSCA March Madness like bracket where you ear points in each race cluster you finish. A race cluster being anywhere from one to four races. If you do well and place first, you get 20 points, and you need a certain amount of points to advance to the next bracket of available races. This allows you to play thru the entire solo campaign more easily and non-linearly than the first game where if you didn't win, you didn't advance.
In the Pro series I played each and every race, won all of them and fished that series with a perfect score (720 points I think). In order to save time in the Champ and SuperRally series, I only bothered to race enough to gather enough points to move on to the next round, but I did finish the solo campaign. But, don't think that it never got tough, or challenging, because it did, especially in the snow rally races in Sweden.
The reason I played everything is due to the all around polish the game has over other such titles as Toca Race Driver 2 and Project Gotham Racing 2. The standard of visual quality in RC2 of Toca2 is an order of magnitude, while the difference between RC2 and PGR2 is not as pronounced. In many ways RC2 is just a dirty version of PGR2 with a way more organic feeling with all the dirt flying around, and with a boost in graphical realism.
Toca2 has a pretty wide range of racing styles, and within it's own universe of rally racing, RC2 offers ample variety. Hill climbs, rainy nighttime rally racing, downhill dirt fests, stadium ice racing, mud with standing water, leaf covered tarmac, etc. All of this variety is underscored with pretty well designed and well implemented environments that very much feel like the English countryside, or the cliffs over Monaco, or the snowy forests of Sweden. Add in the elevation changes, and you get something that is much more interesting than Project Gotham Racing 2.
On the other hand, the variety of cars leaves something to be desired (for me anyway). I may be ignorant about rally cars, but for the most part, many of the cars feel, drive and act the same. The Suzuki loves to get sideways, the Volvo 240 loves to bounce, the Tacoma is nice and fast, and the 206 T16 looks like an ice cream truck. Besides these examples, there isn't much car variety.
For those who want to play online, you really should (and are pretty much forced to) play the offline campaign to unlocks the cars you will need to be competitive. The Supra and the Saab are fast, and if you are puttering along in the Opel (which has the most awkward sounding clutch/shifting mechanism), you are going to lose. I liked being able to onlock everything in Toca2 (for a price of course) without having to finish the solo campaign (which is a lot harder than the RC2 solo campaign, imho).
Also, for the online play, more than four player races will be automatically set to wireframe mode, and the wireframes are stylized, and extremely distracting. If collisions were not turned off, a 16 player rally would be a terrible racing experience, so I think they made the right decision there, but the wireframes are just horrible. Also, they totally screwed the pooch on the voice communication while racing.
You can only hear who is directly in front of you, and directly behind you while racing (in the lobby you hear everyone). If you are third in a 10 player race, you can only hear and talk to second and fourth place racers. It makes it really tough to have a conversation with anyone due to the many position changes that occur in most races. what's worse is that the leader and last place racer will only hear who is second or in front of them (respectively). This MUST be fixed imho, and setting it to be three people in front and behind would be a huge improvement. I suspect bandwidth issues are at play here though, and I have no hope for a change.
The bandwidth is, I believe, being sucked up by the car telemetry. As far as I can tell so far, the position of cars while racing is more accurate than it is in PGR2. Quite often, I will get bumped or bump someone in PGR2 and that situation played out differently on the other person's screen where the bump was more significant, or no bump happened at all. I have yet to experience that in RC2.
The online scoring is similar to PGR2 where your points only go up, and really are just a measure of how much you play the game. There is no ELO rating to tell you who is really good or really bad at the game, so it's hard to be a stat whore in this game, and I think that's for the best.
Last, I want to mention that the XSN integration in the game is very interesting, and I wish more games had it. It's too bad XSN is being shelved for the next year because it could enhance other games that aren't necessarily sports (eg, Crimson Skies). The organization of rally racing thru XSN allows for competition when you, as an individual, have time to compete. This is a great addition to the game and is a should be significant factor in your decision to buy a racing title for the Xbox. PGR2 and Toca2 are both worth the price, but the newness and overall polish on RC2 has resulted in RC2 getting all of my racing play time.