i've been playing this for a bit on my xbox. I really like it! It grabbed me in a way that Outrun 2 never did. I never really gave the heartbreaker mode in O2 a chance, mainly because I couldn't get the handling down in the game. Not a problem with 2006; I got the hang of the handling right away.
Graphics are pretty nice, but for some reason I want to say O2 looked a little sharper. I haven't played it in some time, but its just the feeling I get when playing 2006. No slowdown at all, and no real pop in of the backgrounds. The only weird thing is after you choose which route you want to take next, when the new background first shows up, it sort of "grows" really quickly in the background. Its sort of hard for me to describe, but its like the background is scaling towards you 10x faster than the foreground/track. It only lasts about a second though, so it isn't that annoying. I don't remember if the old O2 did that or not.
I've been putting a lot of time in on the single player part and completed 3 of the 4 flagman circuits and almost am done with the first girlfriend circuit. My only real complaint about these is that there really aren't enough variations between different maps and objectives to keep it fresh over long play sessions. They try to mix up the routes by throwing O2 and SP tracks together, or reversing them, but there really are only 30-some tracks. More than enough for doing outrun mode, but when you keep doing race after race and challenge after challenge, they wear out quickly.
Overall, it does a great job of carrying on the Outrun name and I like it significantly more than Outrun 2.