Dude, you're great. How to say it in Japanese?

You are great, ぉはすっげーぉはすぃね. If you are very familiar with it, you don't need honorifics, but colleagues in the company or people older than yourself must use honorifics. )

You will wonder why I don't translate big brother. The expression big brother is rarely used in Japan. If you don't know someone, say you are really great, you are awesome, don't add your name in front, or ask the other person's name first. If you know someone, say the last sentence name+さん, and then end with respect. If it is a brother, add a "brother"/"elder brother" before it, and then end the honorific.