We have observed 44 planetary nebulae (PNe) in the direction of the Galactic bulge, and merged our data with published ones. We have distinguished, in the merged sample of 164 PNe, those PNe most likely to prtain physically to the Galactic bulge and those most likely to belong to the Galactic disk. We have determined the chemical composition of all the 164 objects in a coherent way. We looked for stellar emission features and discovered 14 new [WR] stars and 15 new weak emission line central stars. The analyzed data led us to the following conclusions: (1) the spectral type distribution of [WR] stars is very different in the bulge and in the disk of the Galaxy. However, the observed distributions are strongly dependent on selection effects. (2) The proportion of [WR] PNe is significantly larger in the bulge than in the disk. (3) The oxygen abundances in [WR] stars do no appear to be significantly affected by nucleosynthesis and mixing in the progenitors. (4) The O/H gradient of the Galactic disk PNe population flattens in the most internal parts of the Galaxy. (5) The median oxygen abundance in the bulge PN population is larger by 0.2 dex than in the disk population seen in the direction of the bulge. (6) Bulge PNe with smaller O/H tend to have smaller radial velocities. (7) The oxygen abundance distribution of bulge PNe is similar in shape to that of the metallicity distribution of bulge giants, but significantly narrower. (8) The location of SB 32 (PN G 349.7-09.1) in the (V_lsr, l_II) diagram and its low oxygen abundance argues that it probably belongs to the halo population.