Here is a link that lays out the basic differences in excruciating detail. (But note the cute little dig at the end).
http://www.ocf.org/OrthodoxPage/reading/ortho_cath.html
Theologically the Roman Church is pretty close to the others. The main theological differences are in the subtle idea of whether the Holy Spirit proceeds from the Father (Orthodox) or the Father and the Son (Catholic) and the concept of the Immaculate Conception of Mary, which is rejected by the Orthodox Church. The Orthodox don’t like the idea of papal infallibility in that they think that big decisions need to be decided in a synod. The stuff about icons, vestments, and even married priests is not considered relevant to the theological dispute and in fact, for the “Uniate” churches, which are former Orthodox parishes now aligned with Rome, the rites and customs are almost identical to Orthodox rites and customs down to married priests.
On the other hand, there is a lot of history between the two that will be harder to overcome than the theology. Greeks blame Rome for the sack of Constantinople in the 13th century, which they feel so weakened the Byzantine state that it never recovered. Russians are suspicious of Catholics through their historical relations with Poland (especially), where Poles established Uniate churches in any formerly Orthodox areas (such as western Ukraine and Byelorussia) that they controlled.
There is a commission that has been set up to try to bring the churches into communion. Right now they are not, which means that Catholics can’t take Communion at Orthodox Churches and vice versa. But it could come.
Interestingly, there is also a movement for the Anglican Church to join the Orthodox churches as an Orthodox congregation.