I just went to Best Buy and played around with the Samsung Galaxy S6 and S6 curve.
First, I'll get the S6 curve out of the way quickly. Personally, I would not get the S6 curve over the regular S6. I don't think the added features are that great and it makes the screen seem smaller. On top of that, it is not comfortable at all to hold.
Now the S6. I am impressed and disappointed all at once. First, it is a beautiful phone that is very comfortable in your hand. I want to emphasis the comfortable part. I was actually surprised how comfortable it is. The screen is beautiful but I'm not sure if it is that much better than the S5 screen.
I'm also concerned about the battery life. Best Buy did not have it plugged into a charger. They had wireless charging pads around there. It went from 100% to 95% in about 5 minutes. The brightness was high and I'm sure practically everything was turned on so I'm not sure how in real world it will be. However, I asked the Samsung rep about the battery life and he said it is excellent because of being able to turbo charge it so quickly. I thought this when watching the announcement and again when this rep said this but the fact that Samsung is emphasizing how much you can get charging it for 10 minutes, battery life is probably not going to be great.
Lastly, I'll mention software. The stock Samsung apps (dialer, message app, etc...) look really nice and I really liked the Samsung keyboard. For the most part, it ran very smoothly. However, it is not completely free of lag. I especially noticed lag in Chrome.
Overall, if you are a fan of Samsung Galaxy phones, I think you will like this a lot. Touchwiz, which is a little leaner, is still a lot like the Touchwiz of old. I don't think the S6 is as dramatically a change as people are making it out to be. Imagine the S5 in a glass and aluminum body with some minor changes to the software. If you did not care for the S5 or S4, you are not going to like this phone.
After playing with it, I think I will wait and see what else comes out this year before buying this phone.