We discuss Bose-Einstein condensation (BEC) in quasi-2D trapped gases and find that well below the transition temperature Tc the equilibrium state is a true condensate, whereas at intermediate temperatures T<Tc one has a quasicondensate (condensate with fluctuating phase). The mean-field interaction in a quasi-2D gas is sensitive to the frequency w0 of the (tight) confinement in the "frozen" direction, and one can switch the sign of the interaction by changing w0. Variation of w0 can also reduce the rates of inelastic processes. This offers promising prospects for tunable BEC in trapped quasi-2D gases.