I really like Atom Heart Mother myself (you might be able to tell this

). I firmly agree with architect's description of the album, it's mellow It's a very 'English' album too, from the pastoral countryside feel and the cow on the album cover to the brass in the title track and the bell sound effects in Fat Old Sun.
The title track is good for the most part, with some really strong sections (Breast Milky and Funky Dung both feature some good), the noises in Mind Your Throats Please I could do without. Overall I think it works, and for me this is where the 1970s Pink Floyd starts to really take shape, before their quintessential sound would be solidified on Meddle.
The three middle tracks are all good, enjoyable tracks in different ways - I tend to consider Fat Old Sun my favourite (I think it captures that 'summer day in the countryside' feel best, and I like Gilmour's guitar solo a lot) but the other two are of a similar standard. If is also quite significant as it features Roger Waters' first lyrical references to insanity.
I must admit I love Alan's Psychedelic Breakfast, hearing Alan speak about his breakfast just makes me smile (marmalade...I like marmalade etc.), it's good to hear Pink Floyd doing something humorous but unlike Seamus and Several Species of Small Furry Animals it's musically strong, especially part two Sunny Side Up which features some gorgeous steel guitar by Gilmour.