I did all these with Eraser on Pro. I'm not sure how much gameplay differs between each player (such as track sloping and placement of cars, etc.)
Apex in the Circle:
It was all downhill, but a lot of the "cars" didn't really correspond with the music. You'd expect there to be less traffic than there was. Still it was interesting to play and wasn't that difficult.
Grip:
Most of the time the music didn't line up with what you hit in the beginning; didn't really make much sense. Throughout the rest of the song it didn't really either, but that was no doubt due to the unrecognizable rhythm. Mostly downhill, going uphill just for a couple seconds now and then. The last downhill section was quite intense and was difficult. There weren't as much red cars as you might expect until you get towards the end. Anyway, overall, as you said it was erratic but fun.
Shape Memory Alloys:
Simple, easy. A lot more traffic than you'd think there would be but (for me anyway) all the colors were pretty well grouped together. This would probably work better as a warm up than Apex in the Circle.
Complete Physical:
lol got 50,000+ points. This one was easy. Starts uphill as you said and stays mostly downhill the rest of the way. A lot of reds and colors are grouped together. Not very difficult. However, the "cars" do line up quite well with the music here.
Boil Down Acid:
Boring. Mostly uphill, very little traffic.
Hoggishness:
First half is uphill, second is downhill. Not hard, but not easy either. Turns out pretty decent. ~
Dooryard:
Starts out uphill and goes downhill. A small uphill at the end. I wouldn't go as far as saying it was difficult, but it sure wasn't easy. A lot of traffic on this one.
Ambiguity:
You were spot on. ~ Track is pretty similar in shape to Dooryard.
Trans-Am:
This one was interesting. I didn't think I would like it because the beginning was quite boring. But the traffic grew with the layering of rhythms and started to get more fun. There was a good amount of traffic but the colors were all grouped together making it pretty simple. Even still I found myself overfilling a lot, not sure why. This would probably be a good one for competition.
Junk Mail (KH Mix):
It wasn't as intense as it should have been. It was mostly uphill (i.e. slow). It goes downhill for two short periods of time, but when it does it's rough. The rest of the song is pretty simple. Track design isn't how it probably should be, but I guess that's what you get for a $10 game.
Smash and Grab:
Ridiculously easy. Even though it's actually all downhill rather than uphill (again, the opposite of how it probably should be) colors are most of the time grouped together. The beginning and various other sections just had a ton of the same color in a row, so staying in one lane for a while is no problem. I got 80,000 points. D: Again, I have no idea if gameplay will differ for each individual so this may not be the case for everyone else.
Servizio:
Eh, this one seemed rather boring. Started uphill for a little while following the rhythm, and then just stayed downhill the whole time following basically the same rhythm but with more traffic. Pretty easy, but not a lot of points to be gained here.
Routrove:
While I didn't like the song, this was imo the best one so far to play. The traffic went along with the easy to follow rhythm, but even still it wasn't easy to get the colors you wanted. It was difficult without going over the top (i.e. insane). It was downhill most of the way and at times, especially the end, went quite fast.
Insurance Money:
Another downhiller. It was quite difficult at first, but once you get the pattern it just turns into a point-fest.
X-Axis:
Mostly uphill, nothing special.
9:
I couldn't seem to concentrate on this one, so I didn't do very well...
But your description fits pretty well. ~
Circulation:
Fits your description fairly well. This seems to be the only one so far to follow the way the song is supposed to.
Apex in the Circle:
Downhill most of the way. The song is really repetitive so it gets a bit boring to listen to. There's a lot of traffic and it's seemingly random and I can't figure out how a lot of it is supposed to line up with the song, so you just kind of tend to ignore the music and just try and group colors together the best you can.
The music doesn't have as much effect on the course as you seem to think it does, but in general it still turns out the same, just to a smaller degree. There were a lot of times it didn't seem to follow any sort of rhythm, but as I said, it's a $10 game, so I suppose every once in a while it can be overlooked.
In short, most of these were pretty fun, but a few don't seem to work too well with this.
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