A muddy muckup...
Where MTM2 went wrong was mostly all related to its gameplay, notably the physics. It was the physics, or the semblance of actually driving a monster truck, that made the first MTM shine. That version's graphics were also apparently good for the time, along with a decent difficulty level (at least if the singleplayer mode were set to 'Professional'). But with MTM2, I feel that the developers got it all wrong. Rather than keeping or improving upon the original physics engine, they completely changed it somehow for the worse. Rather than feeling like I was driving a huge, fat-tired behemoth on nitro, I got the impression that I was piloting a lumbering Lazyboy reclining chair. The feeling was just not there. Also, for some inexplicable reason, they mucked up the racer's perspective, i.e., the race cam. I found the cab of the truck (set to the default chase setting) to interfere with my ability to see the track properly. Ultimately, I fiddled with the different views and found none of them to be satisfactory.
Where MTM2 got it right was in the vastly improved graphics and additional trucks and racetracks. The sound was another big improvement; the revving engines sound spot on to me. And with the second version, we're treated to damage modeling effects, which were nicely done for the time. But these things alone don't make for a great game. Something the original MTM was and still is.