Translation:The huge park has many small trees.
To me, "eta" feels smaller than "malgranda".
But there are words that are opposites that have their own words - for example, "frida" for "malvarma" (usually used only in "fridujo" nowadays).
Some people, especially poets, like to use a wider variety of "non-mal words", coming up with things such as "olda" for "maljuna". Not all of them are widely used, but some do cultivate such a style.
For a list, see (for example) https://eo.wikipedia.org/wiki/Antonimo , and for a shorter discussion of several alternatives, see http://bertilow.com/pmeg/vortfarado/afiksoj/prefiksoj/mal.html#i-6a5 .