My issues with NASCAR:
1. Going in a circle means that by lap 200 the leader is somewhere in the middle of the pack. Most other events that involve racing have a clear cut leader that you can see and gauge how much of a lead they have on the next racer, etc. Just look at the Olympics swimming or running events. There is nothing more exciting than seeing the guy in front and seeing if the other guys can catch him before he reaches the finish line. Not easy to do in NASCAR.
2. Again, since racing in a circle (oval, technically), it means that all the turns are exactly the same. Look at the LeMans race (different turns - sharp, medium, slight, etc), rally racing or the Dakar desert rally require a navigator to help negotiate the different turns, dips, etc. Less skill required in NASCAR turns than those other races. NASCAR would benefit from more varied courses than just that boring oval.
3. Not much diversity. Hard to get into which driver I like when the only differentiator I can see is what type of beer sponsors them.