I can. I recently roasted up two batches of beans -- some El Salvadoran and some Costa Rican. I roasted both to a Full City (dark) roast level. They were very different. I finished the Costa Rican quickly. It was delicious. I'm struggling to finish the El Salvadoran. I'm terrible at describing flavors, but I'd say it's sour with a tea-like flavor.

There's a lot that goes into the flavor of coffee. The beans themselves of course. Brewing technique has a big influence as well. But also growing conditions (altitude, soil composition, rain/sun mix, etc.), processing (wet vs dry process, fermentation time, etc.), handling and shipping (dry or moist conditions), and probably more I don't know about.

I strongly prefer wet-processed beans (mostly south American varieties) over dry-processed beans (mostly African varieties are processed this way). I haven't tried honey-processed yet.

Green beans stay "fresh" for a really long time, but once roasted beans become stale quickly. I can taste the difference between my roasts a day or two after roasting vs days or weeks later.

Yes, absolutely. The other thing to note is that you cannot roast two different beans “the same way”. They do not roast the same. You could roast two to the same degree (same final temperature, or final color), but the way that two wildly different beans absorb heat is going to be radically different. Density of the bean and the internal moisture play a huge role in this. Denser, more moist beans will roast slower and require more heat. Likewise, less dense beans will roast more quickly and may be subject to defects relating to essentially scorching if the same amount of heat is applied.

I roast coffee at a… semi professional level, and I would say that roasting can only make a coffee worse, it cannot be additive. You only bring out the flavors of the origin beans, and if you do it wrong they will taste bad. You can’t make certain coffee taste like fruit, for instance. It just doesn’t exist in the origin coffee.

I am currently drinking three different coffees, and they have three wildly different flavors. One has a very low body, tea like, and earthy flavors. One has a chocolatey cocoa flavor, and one tastes like syrupy rich body with ripe cherry. It’s absolutely unmistakable.

With some, yes. The really obvious ones are fruity vs the more aromatic spice flavours. I can't tell regions apart and I'm unlikely to pick up which specific fruity flavour a coffee is meant to have - stonefruit vs berry or whatever.

The biggest problem I have when trying to run blind taste tests is that different beans behave so differently that it's hard for me, with my low level of skill, to prepare them the same way. I can pack a basket exactly the same with a coffee of roughly the same roast put through the exact same grinder setting and then extract them for the same length of time, but one coffee will consistently come out underextracted for some unknown bean-related reason. In that case you'd just pick up the difference in preparation rather than the flavour of the beans themselves.

Yes, although roasting them exactly the same way is probably not a great idea. But you can roast them to a similar level.

It can be quite a subtle difference, and part of the flavor might also come from the way they process the coffee before it gets roasted (washing the beans, letting them sit in the fruit a little longer, etc.)

But I am sure many people can taste the difference between a costa rican and an ethiopian coffee, as long as it's not roasted to charcoal level. That might influence why people ask this question. A lot of coffee people drink is roasted so dark that there's probably no big difference anymore. Additionally it's often blended. I guess it's how you guarantee a consistent flavor (and bottom line).

Yes, single origin beans from different countries taste different. Colombia is really sharp. Kenyan is more complex. Honduras has a good balance. Ethiopian has a couple of sub-varieties that taste very different from each other. Overall, Ethiopia still makes the best coffee in the world.

I do think I can tell between robusta and arabica. I am not sure about two arabica. Probably not.