There are 425 pokemon that can be aquired in each version (diamond/pearl) and the 2 versions combined have 450. The only pokemon you cannot get in both versions combined are every single starter pokemon and legendaries from all the previous games. (and 3 event pokemon) The game is big though, and the towns are bigger. As for the 8 badges, thats just pokemon for you. It fits the standard layout. God and Silver had 16, but geting the 8 from the Kanto region doesnt take much longer to do than exploring the new area you get after beating the elite four in Diamond, Pearl.
A delayed game is good someday, a bad game is bad forever.