This chapter contains four sections:
The Mishna in Pesachim 53.1 teaches: "In a locale where the custom is to eat roasted meat on the night of Pesach one does so. In a locale where the custom is not to eat one should not." The reasoning here is based on the fact that the Pesach sacrifice is only eaten when prepared roasted on a spit above the fire, and not in pot or boiled in water. Therefore, as people might think that one is eating a Pesach sacrifice in this era [when the Temple no longer stands] outside of its appointed area [Jerusalem], the stringency has been adopted to refrain from eating any roasted meat on the Seder night, even from animals which could not be brought as a Pesach sacrifice.
Those who have this custom pass it down to their descendants. Upon this the verse "Listen, my son, to the reproof of your father..." is applied. (Pesachim, 50.1). Our countries are those in which the custom not to eat is practiced. This only applies to actual roasting directly above fire, and not what is called "Braten" [a type of marinated pot roast made in a dish in an oven or a pot on the stove].
Dry roasting in a pot would appear to be permitted since a Pesach prepared in such a manner would be invalid, as the Talmud states (Pesachim 41.1). Although there is something of a dispute in the Talmud over this issue it is only regarding whether one receives lashes for the transgression, though all opinions still maintain that the Pesach is invalid, as it is not 'roasting over the flame' (Tosafos entitled "Ikah..."). The Rambam writes similarly in the eight chapter of the laws of the Pesach sacrifice, see there. In fact, were one to roast and then cook the meat, or cook and the roast the meat, it would be permitted to eat, since a Pesach cannot be prepared in this manner (as the Rambam writes).
Later authorities write that dry roasting or cooking and then roasting are forbidden to eat. This is because the term 'roasted' is used to refer to that meat (Magen Avraham and Chok Yaakov). Still in all, I do not see why it is necessary to be so stringent for what is essentially a custom, especially without a compelling reason. They do propose a proof from the words of the our teacher the Beis Yosef in section 2, where he writes that "even the meat of a calf or fowl, or any animal that requires ritual slaughter [Shechita], may not be eaten roasted in a locale where roasted mean is not eaten." This, however, does not seem like a correct proof text, for when they accepted upon themselves not to eat any meat that was roasted they nevertheless meant roasted in a way which would be acceptable for a Pesach sacrifice, and not in a manner which would be invalid. This requires further study.
Even in a locale where roasted meat is eaten one does not eat a goat or sheep that was roasted in its entirety since this is far too similar to an actual Pesach sacrifice, prompting people to assume that sacrificial meat is actually being consumed out of its permitted precincts. If, however, it was cut up, or a limb was cut from it, or one of its limbs was cooked even while attached, it may be eaten where the custom permits. This is true even if the animal was only missing its intestines, for it then does not appear to be a Pesach sacrifice. This paragraph follows the intent of Rashi on Pesachim 53.1, where he writes: " 'Mekulosin'...it's head, over it's hind legs and innards [entirely]". See there.
In our communities we do permit roasted fish and eggs as they are not considered meat. However, the liver, spleen and intestines are considered meat and are forbidden roasted, as can be evidenced by the ruling regarding vows in Yoreh Deah, chapter 217 (see there). Accordingly, it is forbidden to eat liver on the Seder night, as it can only be made kosher by roasting (salting is not sufficient), though it is possible to permit it if it was subsequently cooked or fried in fat (after roasting).
There are those who 'exceed the measure' by forbidding even a roasted egg, but there is no reason for this (Taz, comment 3).
It is proper not to eat and drink excessively during the Seder, so that eating the Afikomen Matzah will not be glutinous or forced, for eating the Afikomen should not be a burden (see Magen Avraham, comment 2).
Our custom is to eat an egg as a symbol of mourning, since the day of week the Seder falls out on will also be the day of the week Tisha B'av falls out on later in the year, as is known. It is also a remembrance of the destruction of the Temples, where the Pesach sacrifice was brought, which we are now bereft of due to our sins.
Some have the custom to refrain from any dip on this night, with the exception of the two dips required by the Seder. They therefore eat meat without any dipping in any sauce.
One should be careful to avoid excessive alcohol during the meal in order to avoid being caught by sleep and missing out on reciting Hallel and the remainder of the Seder service. A wise man who has 'eyes in his head' understands the great holiness of this night and carries out the Seder [in a proper manner] with great joy.