In this paper, we introduce a new class of Finsler metrics that generalize the well-known $(\alpha, \beta)$-metrics. These metrics are defined by a Riemannian metric $\alpha$ and two 1-forms $\beta=b_i(x)y^i$ and $\gamma=\gamma_i(x)y^i$. This new class of metrics not only generalizes $(\alpha, \beta)$-metrics, but also includes other important Finsler metrics, such as all (generalized) $\gamma$-changes of generalized $(\alpha, \beta)$-metrics, $(\alpha, \beta)$-metrics, and spherically symmetric Finsler metrics in $\mathbb{R}^n$. We find a necessary and sufficient condition for this new class of metrics to be locally projectively flat. Furthermore, we prove the conditions under which these metrics are of Douglas type.