(no, this is not an editorial on how they look different because frankly, they don’t.)
Yep, probably the first thing that came to mind when you first laid eyes on Son Goten was “Wow, he looks just like Gokuh.” Following the initial observation, you soon also realized that he had a few Gokuh-like qualities: innocence and ignorance. This unfortunately led to the mistaken conclusion that “he is just like Gokuh.” This is far from the truth in looking at several examples.
From a very early age, Gokuh demonstrates a great sense of maturity and responsibility through his actions. Goten, in many situations, demonstrates a childish nature through his amusing antics with his best friend Trunks. He has a rather whiny attitude and is found constantly bothering people with his “ I want more juice” and “ I need to go to the bathroom” remarks. These complaints, though both from scenes added into the cartoon (filler), reflect the lack of independence that Goten has, probably as a result of his overprotective mother. When Gohan and Goten were sparring, upon the instance that Goten had first showed him his Super Saiyajin transformation, and Gohan realized that his little brother was unable to fly, Goten threw a bit of a tantrum and demanded that Gohan teach him to fly as well. This demanding attitude is obviously not a part of Gokuh’s character.
Another major difference between the father and son would be that while Gokuh always concetrates on the bigger picture and does whatever he can to help, Goten’s motivation centers more around his own amusement. When Buu first became a threat, Gokuh recognized the danger immediately and was ready to be entirely focused and serious about the situation. Goten and Trunks' reaction was anything but serious. After being informed of the situation from Videl, they were extremely excited and apparently believed the whole thing would be great ‘fun’(?). Even after Buu had killed Vegeta and supposedly Gohan, Goten was still concerned with how silly the fusion dance looked and how he would much rather be a Super Saiyajin 3. We know good and well that Gokuh has rarely been rebellious to strange training even in less grave situations.*cough* Master Roushi *cough* King Kai *cough*
Unlike Goten, Gokuh is the epitome of independence and has a strong sense of justice and duty. When Gokuh had to suffer the death of his best friend, Kuririn, during the Picollo Daimaoh saga, he got MAJORLY P.O.ed, then went right off to get the source of the problem and killed Tambourine. This he does on all other occasions of death during the Dragonball/Z series. Gokuh always takes action and does his best to improve a situation. When Goten first found out that Gohan had died (well he didn't really that time), he began with about 5 minutes of crying his eyes out, then came close to blaming Gokuh for it, and then was reluctant to learn the Fusion Technique, possibly his only means of taking revenge for his brothers untimely ‘demise’.
In mant respects, I believe that Gohan is more like Gokuh than Goten is. Though he was a bit wimpy and sheltered, Gohan quickly learned to take responsibility for his actions and that protecting the ones he loved mattered more than anything. He has the same innocence and commitment to justice that Gokuh has, as well as the compliance to training and respect for his superiors. Of course, Gohan lacks the confidence and self assured attitude that his father has, and Gokuh lacks the education and well worded manners that his son has. However, they are still more similar than Goten is to Gokuh.
Do not get me wrong. This was not made as an all out Goten bash at all. I like Goten as well as the next fan and he and Trunks as a duo are very enjoyable to watch, their immaturity actually adding to the effect. I am merely outlining the differences between two very different characters that have commonly been considered the same because Goten looks like Gokuh’s clone and they wear similar clothing. Goten was only made to look like Gokuh because Gokuh was dead and Mr. Toriyama wanted him to just remind us of the deceased main character. END!