I picked up each one of these as they came out. Asphalt seems to have people playing now and again, but everyone is running end game cars, so it's tough to get into from a fresh install. People do seem to show up though.
Modern Combat died *fast*. I didn't get more than a couple games in over a week before I stopped seeing people.
It seems like everyone waits for a Nova server to pop up before they join in. I've been able to get a decent sized game going just starting a server and waiting. After a bit, you'll usually see one or two people connect, then a few more flood in after a game or two.