There seem to be a few fairly obvious holes in the current unit roster, that the new beta 4 units won't fill..here are the ones that seem obvious to me...
Forest domination unit
Odd that we don't have any unit with either a large strength bonus in forest (+2 or more) or a stack bonus of +2 in forest. Forest seems to be the second most common terrain (after open), so can we have a forest specialist please? Hills and open have gotten all the love for some reason.
Siege 3 unit
Cities can give a wall bonus of +3, so why no siege units that reduce this bonus all the way to 0? It isn't like this will make cities a pushover, since the ability to have a stack of 32 units is the really scary aspect of a city.
Defender
We have a couple of units with attack bonuses, but no defense bonus unit. I'm not hugely excited by the idea of a dedicated defender, but it does seem a little odd that none exist.