There are three main types of objects: Obstacles, Hazards, Structures, and Puzzles. Some objects could fall into multiple categories.
Obstacles are small objects on the map that you have to slide around when navigating. Most obstacles are just part of the landscape, though some are not natural objects. Obstacles include stones, bits of wall, trees, sign posts, etc.
Hazards are parts of the landscape that could kill you. Some of these, such as spikes, could also be considered obstacles as you have to slide around them to navigate the map. Other's, such as ponds, are not necessarily obstacles as you can slide over them quickly as long as you don't stop.
Structures can be any number of things. In this game there are many decorative structures, many of which come with features such as extra coins or items.
Puzzles are interactive structures that that either unlock something in the game or contribute to the real world mystery set up by the creators of Land Sliders.