I don’t know! I don’t do any promotion at all other than to post about it in online forums.
I do have some theories, though: (for my biggest hits)
Wurm Online
We initially got a some of exposure from Sun, giving us an early player base with somewhat influential people, including several “real” game developers.
I also think it’s a game that fills some kind of gap, which is why we made it in the first place.
Left 4k Dead
I’m a bit stumped… I think using that name helped a lot, plus it’s really accessible.
Infinite Mario Bros
I tried hard to copy the feeling of controlling mario in the original games. I think people are quick to try games based on games they love, and if it feels similar, you get a LOT of free publicity. (It didn’t feel right, though, so I released it as public domain)
During the peak of its popularity, I put a wurm online banner on the top of the game page, and for a few weeks 20% of all new visitors on wurmonline.com came in via Infinite Mario Bros.
Miners4k
I guess this is actually a Good Game™. It’s probably the most original game I’ve made, but it’s still based on familiar concepts (worms, lemmings, diggers).
Breaking the Tower
Again, familiar concepts (gather resources, build houses, kill the enemy). Combined with some minor puzzle solving and a fairly slow pace, it lead to a great time killer for people either bored, at work, or both.
Adding the highscore list led to a lot of people trying to speedrun it, but of course, also to a lot of cheating.
And, some “failures” that I think SHOULD have been hits, but weren’t:
Blast Passage
I assumed people loved bomberman, and that people loved gauntlet. I know I do.
Obviously, the game isn’t as good as I think, and I can’t quite figure out what’s wrong. Perhaps it’s too complicated? Perhaps it’s too plain?
MEG4kMAN
There are almost no hits on this game on google, just this forum and java4k.com. Normally, I’d expect the game to have spread by now, but it didn’t for MEG4kMAN.
My theory is that, since I tried something new, I made something I’m not used to doing, and it shows.
It might also be a bit too difficult.