Wish has few spesific keywords that it accept. You can enter the type of any monster (Sphinx, Nataraja, Doom Horror). This can cause problems as well: typing in "Priest" gives you one independent Priest.
Almost all summoned creatures appear as units (or soldiers), and you need a commander to move them or position them for battle. You can only make them commanders (and use their magic) if you cast Gift of Reason on them. Gift of Reason is Enchantment spell, and you can't Wish for "Gift of Reason".
Doom Horrors appear as commanders. Doom Horrors are dangerous to call for, will disappear after a while, at least one doesn't move from the province it was summoned into (AND it causes feeble-mindedness!).
There are few spesific words that cause special things. 'Armageddon' is bad. 'Death' kills the caster. 'Food'/'Supply' gives you items that produce food. 'Gold'/'Money' gives gold. 'Army' gives you lots of useless militia.