Best Arcade game to date, period!
What makes it better than those two (and everything else, for that matter)? It's just downright fun, and it hits all the right areas. From a gameplay standpoint, you can play simple tracks and try to perfect your abilities on them (taking down your friends' best times makes for a constant game of leapfrog) or tackle some obnoxiously complex and difficult tracks where it takes all your skill (and a huge number of faults) just to complete it. Those are two completely different challenges, and that leads to a TON of replay value. Throw in a track editor, and the replay value goes up another 3 notches. Try that on Limbo.
Then there are the graphics. Yes, this game is worthy of the HD label. I discovered this back when it first came out, and contacted friends. Their first reaction was all pretty much the same upon loading up the demo - "Wow, this thing is gorgeous!"
Along with great gameplay and graphics, the game has a fun side as well. Upon completing a track, you don't simply coast to a safe stop. No no, it's nasty crash time, and the game comes up with funny and unique ways to accomplish this. Some of these crashes in the DLC "Big Pack" are even moer amusing than the original. That doesn't even mention the inevitable crashes you will encounter in the course of playing the game. There are all matter of nasty explosions and gut-wrenching virtual body destruction that will make you laugh and cringe at the same time.
Oh, and I almost forgot the challenges. These skill games are a different play mode that you can also use to compete against your friends. The game would be well worth its price without them, but they are fun as well. Imagine riding the bike down a hill, hitting a ramp, then bailing out to see how far you can fly. You get the idea. It's good clean fun.
Simply put, this game is in another league compared to other Arcade games. Try the demo. If you like it at all, buy the game. Once you like the game, get the Big Pack, and enjoy.