I just hate the fact Lego cars will be in sight during regular gameplay. This will ruin the immersion and the realism of the game for me.
Gamers in general who own many sorts of games will not care too much as the game now has another aspect.
Who will be affected will be people who use the platform to simulate racing and make huge efforts to recreate race liveries for a true immersion.
Also those who simulate a car enthusiast experience - this could be painting, collecting or just cruizing and socializing and being proud of your wheels.
This game has always been promoted and accepted as a good quality racing / car enthusiasts game aimed at more mature car people, although a fair percentage of kids also play the majority of people expected a car experience - not a childs toy experience.
Luckily if the Lego cars ruin the whole experience and appear in freeroam and enter events outside Legoland there is the possibility for a refund or compensation as the game has always been accepted as part of a franchise that is much different to Lego land kiddie cars.
Lego speed is age rated at 7 - 14 by Lego, with this expansion a large percentage of the game is NOT as advertised ( E for Everyone). Consumer law can be used to gain a partial refund for the decreased value of the game OR a full refund if you actually don't want it anymore.
Basically if it is not as advertised and if its something that would have prevented you buying it you have the right to a full or partial refund according to consumer law.
Once the expansion drops I will decide if it affects me based on if I see the cars in freeroam or if they have a mechanical advantage that encourages their use during racing ( like the boneshaker) both of those scenarios for me will encourage a refund either in full or partial... we will see how it goes in a few days.

