From what I've seen posted so far on this Forum:
Legal title (as previously posted, is the seller really the owner?).
Clean title (are there any leans or other debts, like from taxes on the property?).
Are there any inheritance deals pending (goes to legal title).
Above issues need to be cleared by a reputable legal professional, and if there is not an established line of trust, by another too.
About the land:
Location, location, location... but still depending on your own perseption of it.
Check with authorities about any iminent plans (highways, developments, deviation of rivers, water and electricity tru lines and so forth... all probably very dificult to check in the DR, but talk to people).
Check noise... all year round, 24/7.
Check contamintion issues... all year round, 24/7.
Check floding history... again, all year round, 24/7.
Check sismic history (talk to the old folks!)
Check if you have a sound ground for building (especially places close to the beach... if in doubt dig!).
And so forth... (just an other way of saying "I'm not sure I listed them all" ).