The most important thing I think we should have in maps these days is a setpiece.
You don't need them in FPS games as the levels are fairly small and non-linear, but for a racing game you need something to break up the flow from standard driving. In the old days this was a jump here and there, but gamers are used to that, so we need a bit of variety.
A good example would be if, in Steven's level, a boat had to be jumped over, the boat, of course would be moving (bobbing?), providing more of a challenge than a standard jump.
Or in my level, if there were spouts of lava to damage the vehicles.
Absolutely MASSIVE jumps would also work, but then there's the problem of getting the players back up to the top.
Not only should these be present, but there should be at least one "grand" set-piece. Think the cannon in DK's level on Mario Kart, or driving up the building at the end of UWRL-SUICIDE, or maybe the giant swinging pendulum in UWRL-Aztec (actually that level was mainly designed as a test-bed for set-pieces and not as a real level, the flow and design are terrible, but the set pieces are fun). There needs to be something that makes the player go "woah!". This is what will set UnWheel apart from the average racer.
Luckily the new UnrealED is pretty much designed with setpieces in mind, so there's no excuse guys!