For anything complex, you'll run into "slow start" issues and have to look at provisioned concurrency.
Lambda also sucks for dependencies. Zips and "layers" can only be so large. Eventually you'll hit the limit and have to move to containers. There are also other limitations, like payload sizes. Eventually you might run into that, too.
Also, it would be nice if Lambda just reused the CGI interface instead of inventing its own thing.