An enigma wrapped in a puzzle
The first letter of the riddle is also the first letter of the solution. Likewise, the last letter of the riddle is the last letter of the solution.
Given the following nonoriddle, lets look at some steps to solve it:

A good place to start notice that one of the columns is going to have four squares filled in. Given that there are only five squares in the column, it can be deduced that no matter which grouping of four squares you fill in, the middle three will always be filled.

With those three squares filled in, you can see that they correspond to some of the across numbers. When you know a group is completed, it is often helpful to mark the square on either side of the group as definitively empty. With this online interface, click a square twice, marking it gold. On paper, many people simply place a dot in the center of the square to mark it definitively empty.

Knowing which squares are definitely empty can help determine which squares to fill in. For example, in the fifth column, there's only one place where a group of two squares can be filled in. In the bottom row, there's only one way to place three one-square groups, each separated by a space.

Now, in the fourth column there's only one place that the remaining filled square can go. At the same time, three definitely empty spaces can be marked: The "L" space in the fifth column (the two-square group is already marked so the rest of the squares in that column have to be empty) and the "A" and "S" squares in the first and third column, respectively.

With that done, in the top row there's a two-square group that needs to be filled in. One has already been marked, so the second one has to adjoin it. Since we marked the "L" square definitely empty, only the other square on the other side can be filled. Likewise, there's only one spot free in the fourth row to put the group of one.

Marking the squares in the top row and the second column as empty leaves us with only one place to put the final square.

Here is the completed grid. We can do a quick verification to make sure all the right squares are filled in by checking that the number of squares filled in each row and column match the numbers at the edges. On the online interface, you can click on the "Verify Grid" to make sure everything is filled in correctly.

Now to the riddle. The remaining letters are "COLOSSUSINASIA". Putting in spaces logically gives us the riddle "Colossus in Asia". We now know it begins with "C" and ends with "A" and is five letters long. The largest country in Asia is "China", and it is also a common wedding gift, so that is the answer.