You've all seen this image, right? That is the difference between older and newer generations. Newer monsters have more 'pointless' features; spikes, stripes, fluffy bits, etc. What's good or bad is a matter of opinion, but there is generally a clear distinction between early and recent generations.
People's speculation on "what x Pokémon would look like if it was made in the year y" besides, the first game were made for a system that could only display sprites with four shades of grey and a total size of about half those in Black and White - let alone the increasingly detailed 3D representations in Pokédex 3D or the console games.
Of course they have more room to include further detail and a greater range of colours in designs now.