When the theme is very restricted, like gunmaster with shields it can get a bit frustrating. Having something like rush and TDM for example mixes it up a bit, the same as something like water maps that could include Shangshite to keep people interested. Some of the lesser used modes are fun for a change.
A lot of the other game modes are fun to play. On some maps though Rush can become a stalemate because of the objective locations. CTF too is a bit like that. Look forward to Gunmaster (with shields) on Zavod Night Shift in the same way I look forward to having prunes and custand.