What this coin looks like (obverse, reverse, mint mark location, special features, etc.): There were two major varieties of the 1846 O Seated Liberty Half Dollar in regards to the size and style of the numbers in the 1846 date. The variety depicted above is the "Medium Date" variety.
The Medium Date features smaller and shorter numbers whereas the Tall Date features taller and larger numbers. The easiest way to distinguish the two varieties is to note the number "4". The Medium "4" has the right-side and bottom serifs nearly touching each other while the Tall "4" has a nice gap between the serifs as depicted by the arrows in the example image below. The medium sized "8" sits lower than the rest of the numbers in the date - but the tall "8" lines up with all of the numbers. The medium "6" has a smaller gap in the upper portion within the "6" and a larger space on the bottom portion. The tall "6" however has a larger gap in the upper portion within the "6" and a smaller space on the bottom. Lastly: The medium "4" lines up vertically more towards the left side of the seated liberty portrait whereas the tall "4" is lined up more towards the right side. These features are depicted below in the example comparison image of the 1846 Medium Date vs Tall Date Seated Liberty Half Dollar:
Coin value chart: Typical coin prices, values and worth in USD based on grade/condition