A sequel is coming for Metro 2033, called Metro 2034
From the IGN article:
The good news is THQ seems to be allocating more resources for Metro 2034. "The sequel's even more advanced in terms of the technology," said THQ executive VP of core games Danny Bilson. "The sequel's going to get a lot more support than the first one got both from product development at THQ and marketing. There were certain things in Metro 2033, even though it looked sensational, some of the shooting mechanics need to be better polished to compete with the Call of Dutys. They are this time. For marketing it'll get a much more respectful push."
"We green-lit it before the other one shipped and you're going to see some of it at E3."