THPS4 doesn't break much new ground, but it doesn't really need to does it?
The most visible difference of the latest Tony Hawk game is definitely the new goal system. Taking a hint from Dave Mirra's FreeStyle BMX, the guys at Neversoft have placed people around the levels that ask you to do things for them. There is no time limit until you find one of these people. After goal is achieved or the mission failed, the timer vanishes again. Framerates seem improved from THPS3 (not that they were really that bad). I only noticed a significant drop once, and the game is naturally unfinished. You have at least one cool new ability--the ability to grab onto a cars bumper for a boost of speed. You have to balance to hold onto the bumper just like grinding or stalling.
THPS4 is basically what I expected; it's a very natural extension of the series and it should give THPS fans exactly what they're looking for.