Just took a look at Season one, it does look a little compressed when played on a standard DVD player, it looks a lot better in a Bluray player being upconverted, either way it's still quite a good image if you don't zoom it.
There's some interesting information on Wiki about DVD Bitrates.
http://en.wikipedia.org/wiki/DVD-Video#Data_rate
It's interesting to note that season two has the same number of episodes but one less disc (yet you say it looks better, I haven't looked at it yet.) so i doubt they had to compress it much on season one.