Actually there were several rectal route drugs available. Both Penothal® (no longer available), and Brevital® could be given that way, in fact at least into the 1970's Abbott Laboratories had a Penothal formulation intended for rectal use. The other commonly used drug until the 1960's was Avertin.
Avertin in still used today for laboratory animals. Avertin is a chemical cousin to Chloral Hydrate. However as Vito pointed out, none of these drugs had significant analgesic properties, so an inhaled anesthetic was used once the patient was 'out'.
These have largely been replaced by inhalation agents like Sevoflurane, which is much more potent than Ether, non-flamable, and has a relatively pleasant odor. These agents are potent enough that a single deep breath is often all it takes to produce unconsciousness.
In certain circumstances both Valium and Versed are given rectally to control seizures. They are also sometimes used to provide sedation.
The main disadvantage of rectal administration of all of these drugs is absobtion subject to large variations, and it is very difficult to adjust the dose, With IV and inhaled agents, this is far less of a problem, and not subject to anything like the variability seen with rectal administration.