Hi Keyser Soze,
There are a number of things that influence the flavour. The cultures you use is one. So, if you're generally using the same starter for all your cheeses, the flavours will be more similar than if you use different starters. Flora Danica, for example, contains strains that help produce a buttery finish, but it's a weak acidifier. The sourness could be excess whey, which means you may need to stirr a bit more, or cut the curds a bit smaller, or both, etc. If you're using store bought milk, pasturized and homogenized, you may want to try a different brand as it could be the milk. It could be the bagging as well, as this prevents the cheese from breathing while it ages. I often find that bagged or waxed cheeses will take a while to "air out" (as in a few days or even a week or more) before their true flavours come through. If you can age your cheeses in boxes, rather than bagging them, this may help (they can slowly expel whey and not have it trapped against the cheese, for example).
For the butterkase, did you use yogurt or a culture for the thermo? Try different yogurts if you're going that way, as each will have their own strain of starters. (Use a plain yogurt, not something like "strawberry swirl", etc).
I'm sure there are other things as well that people will suggest. In the end, though, it's really a matter of practice. As you make more cheeses your technique improves. You'll get a better feel for the curds, and what stage they are at, etc.