If your work isn't being adequately acknowledged and appreciated, that's a major culture problem. I've never felt that my code reviews were thankless. In fact, as I've become a more senior developer on the team, I've found that my code reviews or suggestions can sometimes crowd out acknowledgment for more junior members, so I try to redirect praise where appropriate—code reviews are in my mind the most pure expression of pair programming, where you get a collaborative outcome that's better than either the programmer or the reviewer would be able to achieve independently.