Which Leto Atreides? There were three of them: Duke Leto, the child Leto (Paul and Chani's firstborn who was killed by the Harkonnens), and Leto II, aka the God Emperor.In the end, stories with protagonists a lot of people can relate to, seem to do well. Luke Skywalker, Leto Atreides, Frodo Baggins.. Fantastical settings, and yet, there's so much there in these characters to relate to. Main characters usually go through some sort of a journey, and that's what life is - a series of journeys. I guess in the end the deal is that if the main character is going through a journey I can't relate to at all, then I'll be a bit "meh" about everything. Who is this robot who is going through this ordeal? Who do I care? But if it's someone like the 3 characters I mentioned, it's so easy to see character traits I can relate to very well, which seems to draw me more into the story, because it seems to be written from some place that actually exists.. and I guess it also seems human.
I'm assuming you are not referring to the child who was killed, as he was little more than a baby and most people tend to forget he even existed.
Duke Leto (Paul's father) is one of the Dune characters I really like. Someone who rules a whole planet could easily turn into a tyrant, as the Harkonnens did, but Duke Leto's focus is on honor and justice.
Leto II... well, there are some people who think he's just wonderful. I think he's a murderous, narcissistic psychopath. I absolutely can't stand him. The only character in God Emperor of Dune who is remotely relatable is Duncan Idaho - who happens to be my favorite Dune character no matter which book I'm reading (of the FH ones, that is).