All racing games are linear, in a sense, but Motorstorm was one of the few out there to offer a truly wide racing area with a multitude of potential paths available to the player. These paths were not set in stone either as you could move from one to another throughout much of the race. It was a very open racer. I can't think of anything else quite like that, really. Even stuff like Burnout Paradise, with its open world, ends up feeling somewhat more restricted when actually racing. The courses in Motorstorm were extremely cool. Bringing such open environments to an island sounds awesome.
Motorstorm was all about racing the same type of environment, open track or not in pretty much the same car every round. Without any real vehicle customization or sweet ass cars to unlock, the game became stale as fuck.
Yes, that was its problem...but the core gameplay was rock solid.
There were a limited number of tracks, but each one was extremely different from any of the others (gameplay wise).
You didn't use the same car every round, though. They constantly switched it up and there was a pretty big difference between racing an ATV, a racing truck, and a semi. Customization doesn't matter in an arcade game, if you ask me.
All I'm saying is that they presented the content very poorly, but the core of the game was very good.
I actually think of DiRT as the opposite. The menu is fantastic, the amount of stuff in the game is great, and they offers lots of customization (which would not fit in Motorstorm)...but the core of the game was pretty boring (I thought). DiRT only cost me $8 on the PC, though (Circuit City sale), so I didn't feel cheated. When Motorstorm was firing on all cylinders, it was one of the most intense racing experiences I've ever had. It simply didn't have the content to last.
For me, sitting a few feet from my 50" plasma using the first person view with the SIXAXIS motion control felt really incredible. I know people weren't down with the motion controls, but holding it like a wheel and using the first person perspective could feel really cool. It had issues at times (hood crumpling in your face), but there was so much potential there.
That's why I think the sequel could be truly outstanding.