They are obsolete, but they should still work. On the other hand, they have somewhat different characteristics from silicon transistors. When silicon transistors became available at low cost, most of us put our germanium transistors into the drawer or waste bin.
1) Germanium tend to have significant collector leakage, whereas we tend to ignore this in silicon designs. The leakage has a temperature coefficient that is a problem even at moderate temperatures.
2) Their base-emitter voltage is about 0.2V. Silicon is nominally 0.65V. This isn't really a problem, it's just different. As mentioned, some special circuits use this feature.
3) Most germanium transistors are useless above 85 degrees C whereas many silicon transistors are useful up to 175 Celsius. Storage temperature of 2N1304 is limited to 100 C!!!
4) The maximum VCE tends to be lower. Economy germanium transistors were 25V, while economy silicon transistors are 40-60V.
5) Frequency response (FT) of general-purpose germanium transistors were in the neighborhood of 1-10 MHz. (Specials were made for RF, but they were expensive.) Cheap silicon transistors are usually 300 MHz.
You might look up 2N1304 and 2N1305 to see the characteristics of popular mid-60's germanium transistors.