Criticisms of the Lewis Trilemma have been made. One is that he might be a legend. This largely comes from people who are trying so hard to prove that there isn't a God that fall into their own kind of religiosity. If you have time read Bart Ehrman's book, Did Jesus Exist? He says that it is not only his professional opinion that Jesus existed, but the professional opinion of almost all New Testament Scholars. Ehrman is a high ranking New Testament Scholar and atheist who is more commonly found defending his atheism from Christians than defending Christians, but defending Christians he does. So he gets a lot of credibility when he defend's Jesus' existence from the Mythisists. Or if that's not good enough you could always read the many reasons he gives in the book, but of course, reasons are for suckers.
Another Criticism of the Lewis Trilemma is Space Alien... that Jesus might be a space alien. Hey, it's not more unrealistic than believing he's God, right? The problem with this you're substituting belief in one crazy thing for another. Maybe Jesus isn't Lord, but you have to go all the way to Space Alien to prove it. Why atheists are more comfortable with things like space alien and not Lord is beyond me.
I think the best criticism is one that I never hear talked about. Jesus was inconsistent. When we look at historical figures we tend to turn them into cartoon characters; not a lot of layers. Jesus could have been very profound when he talked about loving each other, and at the same time very loony when he talked about his role in the Kingdom of God. I know lots of people who are fanatical about some things and not about others. Or are liars about some things and not about others. Lots of sensible honest people will say insensible dishonest things about their favorite politician for example.
Liar Lunatic Lord? Or how about just not a cartoon character?