Concrete poetry is one of the more experimental poetic forms available to poets. Concrete poems use space and sound to communicate the meanings of the words. Words can cover other words; and the poem has trouble standing without the structure. Concrete poetry is more visual than other poetic forms.
Of course, concrete poetry has plenty of detractors because of the weight structure has on the words, but as much thought goes into concrete poetry as any other form.
Here's an example:
We line up. We wait for the "set"
and then gunblastexplosionbangandwe'reoff
As you can see from this example, taken from my days of running track & field, the structure gives the poem added weight and importance. Without the structure, this poem would just read:
"We line up. We wait for the 'set' and then gun blast explosion band and we're off running our first circle, our first lap, but the real race starts on the second lap, and then we're tumbling in from first to last."
In the concrete form, I was able to simulate the two laps that an 800 racer must run, which coincidentally forms a figure 8. Also, I can simulate the wait before the gun blast to start the race and the initial jumbled feeling of the start all the way through to the way each runner finishes in a different place "from first to last."
This form can be very fun to write. Of course, you'll need to think of subjects that open themselves up to a certain type of form. You could write a heart-shaped love poem, a scary jack-o-lantern poem. The sky really is the limit (or is it?).